Which Form 1040 does a UK company's 31 March year end go on?

If the UK company's US tax year genuinely runs to 31 March, the period ending 31 March 2026 is reported on the 2026 Form 1040, because the Instructions for Form 5471 require you to report information for the tax year of the foreign corporation that ends with or within your tax year. The closing date is what matters, not where most of the months fell. Before relying on that, check whether section 898 has already fixed the company's US tax year as the calendar year, which it will have done if the company is a controlled foreign corporation more than 50 percent owned by a US shareholder.

Does my UK company have to change its year end to 31 December for Form 5471?

No. Companies House and HMRC are entirely indifferent to your US filing position, and there is usually no UK reason to move an established accounting reference date. The question is not whether the UK date changes but what the company's US tax year is. Where section 898 applies, the US tax year is the majority US shareholder's year regardless of the UK date, and the work is recutting the figures rather than refiling at Companies House. Changing the UK date to match can simplify future years, but it creates a stub period and bunches two periods of income onto one Form 1040 in the year of change.

What happens on Form 5471 when a UK company shortens its accounting reference date?

Shortening creates a stub period on the UK side, and if the company's US tax year is changing too it creates a short period on the US side. Where two annual accounting periods end with or within the same filer year, two separate Forms 5471 attach to that one Form 1040, each with its own dates, schedules and exchange rates. Keep the same reference ID number on both, complete item C at the end of each period separately, do not check item D simply because a period ended, and make sure the Schedule J earnings and profits closing balance of the first period becomes the opening balance of the stub.

What did the 2025 legislation change about controlled foreign corporation tax years?

The Instructions for Form 5471 (Rev. December 2025) record that under section 70352 of Public Law 119-21, enacted 4 July 2025, a specified foreign corporation may not have a tax year beginning one month earlier than the majority US shareholder year, for tax years beginning after 30 November 2025. The instructions describe this as repealing the one-month deferral election previously permitted under section 898(c)(2). Affected controlled foreign corporations have a first required year ending at the same time as the required year defined in section 898(c)(1), and a Form 5471 should be filed for that first required year.

Which exchange rate applies to a non-calendar Form 5471 period?

The rate for the corporation's own period, not a calendar-year rate. Schedule E translates foreign taxes at the average exchange rate for the tax year to which the tax relates under section 986(a), and Schedule M uses the average exchange rate for the foreign corporation's tax year under section 989(b). Worksheet B translates the section 956 amount at the year-end spot rate, which for a 31 March period means the rate at 31 March. Every rate must be reported using the divide-by convention, rounded to at least four places, as the units of sterling that equal one US dollar rather than the dollars that equal one pound.

Form 5471: UK Company With a Non-Calendar Year End

Q: Can a UK accounting period be longer than 12 months?

For accounts, yes. A Companies House accounting reference period can be extended to a maximum of 18 months measured from the start date of the period, once in every five years, with exceptions for administration, aligning with a parent or subsidiary, and special permission from Companies House. For corporation tax, no. GOV.UK states that a corporation tax accounting period cannot be longer than 12 months, and HMRC's Company Taxation Manual at CTM01510 confirms that no accounting period can be longer than twelve months but it may be shorter. Where accounts cover more than twelve months you must file two Company Tax Returns, one for the first twelve months and one for the rest.

Form 5471 is filed for the foreign corporation's annual accounting period, and it is attached to the US shareholder's return for the tax year in which that period ends. The Instructions for Form 5471 (Rev. December 2025) state the rule in a single sentence: report information for the tax year of the foreign corporation that ends with or within your tax year. So a UK limited company whose accounting reference date is 31 March 2026 is reported on the shareholder's 2026 Form 1040, not the 2025 one, even though nine of that period's twelve months fell in 2025. The form is then attached to that return and both are filed by the due date, including extensions, for that return.

There is a prior question that most guidance skips, and it is the one that causes the real damage. Before you map a UK accounting reference date onto a US tax year, you have to ask whether the UK company was ever entitled to a non-calendar US tax year in the first place. For a great many UK companies owned by Americans the answer is no, because section 898 has already fixed the company's US tax year as the calendar year regardless of what Companies House shows. Getting that order of operations wrong produces a Form 5471 that is internally consistent, looks tidy, and reports the wrong twelve months.

What Is the Annual Accounting Period on Form 5471?

The annual accounting period is the foreign corporation's tax year for US federal tax purposes. It is not the company's Companies House accounting reference period, it is not the HMRC corporation tax accounting period, and it is not automatically the period covered by the statutory accounts the directors signed. Those three UK periods can and often do coincide with the US tax year, but they are determined by UK company law and UK tax law, and they carry no authority over which twelve months the IRS expects to see.

The governing definition sits in Regulations section 1.6038-2(e), headed Period covered by return, and it repays reading in full because four separate sentences each do work. The information must be furnished for the annual accounting period of the foreign corporation ending with or within the United States person's taxable year. The annual accounting period is the annual period on the basis of which that corporation regularly computes its income in keeping its books. In the case of a specified foreign corporation as defined in section 898, the taxable year of such corporation is treated as its annual accounting period. And the term may refer to a period of less than one year. Between them those sentences settle the default rule, the section 898 override and the treatment of stub periods.

Page 1 of Form 5471 (Rev. December 2025) makes the distinction unusually visible, because it asks for two separate sets of dates. Immediately below the title the form requests the dates of the information furnished for the foreign corporation's annual accounting period, described on the form itself as the tax year required by section 898. A few lines further down, in a field of its own, the form asks for the filer's tax year beginning and ending dates. Those two date ranges are allowed to differ, and on a UK company with a non-calendar year end they frequently do. A return that shows the same dates in both fields when the UK company has a 31 March year end is either reporting a recut calendar period, which may well be correct, or it is wrong, and only the section 898 analysis tells you which.

One item on page 1 is quietly period-sensitive as well. Item C asks for the total percentage of the foreign corporation's voting stock you owned at the end of its annual accounting period, not at the end of your own tax year and not an average across the year. Where shares moved during the period, that single date drives the entry.

Does a UK Accounting Reference Date Set the Form 5471 Tax Year?

Often it does not. The Instructions for Form 5471 explain that the annual accounting period of a specified foreign corporation, as defined in section 898, is generally required to be the tax year of the corporation's majority US shareholder. Where there is more than one majority shareholder, the required tax year is the one that results in the least aggregate deferral of income to all US shareholders of the foreign corporation. The instructions also give the section 898(b) definition of a specified foreign corporation: a foreign corporation that is treated as a controlled foreign corporation for any purpose under subpart F, and in which more than 50 percent of the total voting power or value of all classes of stock is treated as owned by a US shareholder.

Read that against the typical client. A US citizen living in London owns 100 percent of a UK limited company that trades profitably. The company is a controlled foreign corporation. More than 50 percent of its stock is owned by a US shareholder. It is therefore a specified foreign corporation, its required year is the majority US shareholder's year, and that shareholder files a calendar-year Form 1040. The company's US tax year is the calendar year. Its 31 March accounting reference date remains perfectly valid at Companies House and perfectly valid for HMRC, and it is simply not the period the Form 5471 reports.

The practical test runs in this order.

Is the UK company a controlled foreign corporation, and is more than 50 percent of its voting power or value owned by a US shareholder? If yes, it is a section 898 specified foreign corporation and its US tax year is the required year, normally the calendar year of the majority US shareholder.
If there is more than one majority shareholder, the required year is the one producing the least aggregate deferral of income to all US shareholders, which will not necessarily be any shareholder's own preferred year.
If the company is not a specified foreign corporation, for example where a US person holds a reportable but minority interest and no US shareholder holds more than 50 percent, section 898 does not force a year and the corporation's own tax year governs.
Only in that second case do you apply the ends with or within rule to a genuinely non-calendar period.
In every case, record which of these two routes you took in the file, because the answer changes the twelve months you report and nothing on the face of the return explains your reasoning.

Where a required-year change is needed, the machinery sits outside Form 5471. The Instructions for Form 5471 point to section 898 and to Rev. Proc. 2006-45, 2006-45 I.R.B. 851, as modified by Rev. Proc. 2007-64, 2007-42 I.R.B. 818. The Instructions for Form 1128 (Rev. November 2017) add the mechanical point that where a controlled foreign corporation does not have a US trade or business, the controlling domestic shareholder or shareholders must file Form 1128, Application To Adopt, Change, or Retain a Tax Year, on behalf of that foreign corporation to change its tax year. A foreign corporation that is not otherwise required to have an EIN enters Not applicable in the identifying number space.

The OBBBA Change to CFC Tax Years From 30 November 2025

This area moved recently, and any guidance written before the summer of 2025 is now unreliable on the point. The Instructions for Form 5471 (Rev. December 2025) record that under section 70352 of Public Law 119-21, 139 Stat. 72 (July 4, 2025), commonly known as the One Big Beautiful Bill Act, for a tax year of a specified foreign corporation beginning after 30 November 2025 the corporation may not have a tax year beginning one month earlier than the majority US shareholder year. The instructions state elsewhere that section 70352 repeals the one-month deferral election that was permitted under section 898(c)(2), effective for taxable years of specified foreign corporations beginning after 30 November 2025.

The instructions also describe what that does to the affected corporation's calendar. A controlled foreign corporation affected by the provision will have what the instructions call a first required year, which will end at the same time as the required year defined in section 898(c)(1), and a Form 5471 should be filed for that first required year. Where such a corporation paid or accrued foreign income taxes subject to the allocation rules, the instructions direct filers to Notice 2025-72, 2025-51 I.R.B. 840, or subsequent guidance. For a UK company that had been running a 30 November year end to sit one month ahead of its US owner, this is a forced realignment, and the transition into the first required year behaves exactly like the stub-period problem described further down this article.

Which Form 1040 Does a 31 March or 30 September Period Attach To?

Take the case where section 898 does not force a calendar year, so the UK company's own non-calendar tax year genuinely applies. The rule is mechanical once you accept that only the closing date matters. The period ending 31 March 2026 ends within the shareholder's 2026 calendar year, so it is reported on the 2026 Form 1040. The period ending 30 September 2026 also ends within calendar 2026, so it too goes on the 2026 Form 1040. A period ending 31 December 2026 ends with the shareholder's year, which is why the instructions say ends with or within rather than simply within.

UK period 1 April 2025 to 31 March 2026 ends in calendar 2026, so it is reported on the 2026 Form 1040 and filed in 2027.
UK period 1 October 2025 to 30 September 2026 ends in calendar 2026, so it is also reported on the 2026 Form 1040.
UK period 1 January 2026 to 31 December 2026 ends with calendar 2026, so it is reported on the 2026 Form 1040.
UK period 1 April 2026 to 31 March 2027 ends in calendar 2027, so it moves to the 2027 Form 1040.
The number of months of the period that happen to sit in the earlier calendar year is irrelevant to the mapping, however uncomfortable that looks on a workpaper.

Notice what the 31 March year end does to timing. Profit earned by the UK company in April 2025 is not picked up on any US return until the 2026 Form 1040, which for a taxpayer abroad taking the full extension is not filed until late 2027. That deferral of well over two years between earning and reporting is precisely the mischief section 898 was enacted to close, and it is the reason the required-year analysis has to come first rather than last.

The Off-by-One Error and How It Surfaces in a Catch-Up Filing

The commonest error we see on files we take over is intuitive rather than careless. A preparer looks at a 1 April 2025 to 31 March 2026 UK period, sees that most of it fell in 2025, and attaches the Form 5471 to the 2025 Form 1040. The return balances. The schedules tie to the UK accounts. Nothing in the software objects. But the 2025 Form 1040 now carries a foreign corporation period that had not closed when that tax year ended, and the 2026 Form 1040 will either carry nothing for the company or will carry the same period a second time. Any subpart F or GILTI inclusion has been reported a year early, in a year with different income, different bracket exposure and a different foreign tax credit limitation.

The error is self-perpetuating, because the following year's preparer copies the prior year's treatment. It usually stays invisible until someone has to look at several years at once, which in practice means a catch-up filing. Under the Streamlined Foreign Offshore Procedures a taxpayer files delinquent or amended returns for each of the most recent three years for which the due date has passed, together with all required information returns such as Form 5471, plus six years of FBARs and a signed Form 14653. At that moment the off-by-one becomes structural rather than cosmetic. Three UK accounting periods have to be assigned to three specific Form 1040 years, and if the assignment is shifted by one, the earliest period falls out of the submission window entirely while one period gets reported twice.

There is a related piece of advice circulating in online forums that should be retired: the suggestion that you deal with a mismatch by stitching two part-periods of UK accounts together into a pro forma calendar year and filing that. As a general rule it is wrong, because Regulations section 1.6038-2(e) requires the report to be furnished for the foreign corporation's own annual accounting period. The confusion arises because there is a case in which you do report calendar-year figures for a 31 March company, and it is not this one. It is the section 898 case, where the calendar year is not a pro forma construct at all but genuinely is the corporation's US taxable year. The distinction is not pedantic: in the section 898 case the recut period is the tax year and the figures belong there, whereas outside it a stitched calendar period misstates the period the regulation asks for.

It also shows on the face of the return, which is why it is worth fixing before filing rather than after a notice.

The dates below the title of Form 5471 will not be a period that had closed by the end of the filer's tax year shown further down page 1, and those two date fields sit within a few lines of each other.
Schedule J will not roll forward, because the closing earnings and profits balance of one year will not be the opening balance of the next once a period has been double-counted or skipped.
Schedule P previously taxed earnings and profits will not agree to the inclusions actually reported on the Forms 1040 in the submission.
The reference ID number, whose stated purpose in the instructions is to keep track of the corporation from tax year to tax year, will show a chain of years with a gap or an overlap in it.
Because the section 6038 penalty is imposed for each annual accounting period of each foreign corporation, a period that has been dropped is its own separate exposure rather than a presentational issue.

How a UK Accounting Reference Date Is Set and Changed

On the UK side the starting position is automatic. Companies House guidance explains that a new company's first accounting reference date is the last day of the month in which the anniversary of its incorporation falls, and subsequent accounting reference dates fall on the same date each year. A company incorporated on 6 April 2025 therefore has a first accounting reference date of 30 April 2026, and a first accounting reference period slightly longer than twelve months. Accounts may be made up to the accounting reference date or to a date up to seven days either side of it, which is a small tolerance but one that can move a period end across a month boundary.

A company can change its accounting reference date online, through software, or by sending paper form AA01 to Companies House, and the change can only be made for the current accounting reference period or the one immediately before it. The rules for shortening and extending are not symmetrical.

Shortening is effectively unrestricted. GOV.UK states that you can shorten your company's financial year as many times as you like, and the minimum shortening is one day.
Extending is restricted to once every five years, and to a maximum of 18 months, with exceptions where the company is in administration, where it is aligning its date with a parent or subsidiary undertaking, or where it has special permission from Companies House.
The 18 month limit is measured from the start date of the accounting period, not added to it. GOV.UK guidance states that you cannot extend a period so that it lasts more than 18 months from the start date of the accounting period, unless the company is in administration, and specifically warns against simply adding six months to an existing period.
There are no additional restrictions on changing a company's first accounting reference date, and where a first period is extended to the maximum the date of incorporation counts as the first day of the period.
You cannot change the year end once the accounts for that period are overdue. GOV.UK is blunt about it: you cannot change your company's year end when its accounts are overdue.

That last point has a US consequence that is easy to miss. If a client asks in November 2027 whether the company can retrospectively move its 31 March 2026 year end to 31 December to tidy up the US position, the UK answer is usually no, because the Companies House deadline for a private company is nine months from the accounting reference date and that window closed at the end of 2026. The US analysis then has to be built on the periods that actually exist.

It is worth stressing how little choice sits behind most of these dates. A US founder who incorporated a UK company in March did not select a 31 March year end as a planning decision. Companies House assigned it, because the default first accounting reference date is the last day of the month in which the first anniversary of incorporation falls. The first accounting reference period is then a little over twelve months rather than exactly twelve, which means the very first Form 5471 for that company may be reporting a period that is not a clean year, before any year-end change has even been contemplated. That is a period question on the first return, not something that only arises later.

Can a UK Accounting Period Be Longer Than 12 Months?

For accounts, yes. For corporation tax, no. This is the distinction that confuses preparers most often, and it is worth stating precisely because the same phrase, accounting period, is used for two different things. A Companies House accounting reference period can run up to 18 months from its start date where the extension rules are met, and a single set of statutory accounts can therefore cover 15 or 18 months. A corporation tax accounting period cannot. GOV.UK states plainly of the corporation tax accounting period that it cannot be longer than 12 months, and HMRC's Company Taxation Manual at CTM01510 says that no accounting period can be longer than twelve months but it may be shorter.

Where the accounts cover more than twelve months, GOV.UK states that you must file two returns to cover the period of your accounts, one for the company's first twelve months and one for the rest. So a UK company that extends from 31 December 2025 to 31 March 2027 produces one 15 month set of statutory accounts, two corporation tax accounting periods, and two Company Tax Returns. For the US preparer that matters because the UK tax figures that feed Schedule E do not arrive as a single annual number, and because the UK profit has been apportioned between two periods under UK rules that have nothing to do with how the US tax year is cut.

Two further UK dates are worth holding in the same file. The Company Tax Return is due twelve months after the end of the accounting period it covers, and for a company with taxable profits up to 1.5 million pounds the corporation tax itself is due nine months and one day after the end of the accounting period, with instalment rules applying above that threshold. Those dates determine when a reliable UK tax figure exists, which in turn determines whether a Form 5471 Schedule E entry is a computed number or a placeholder that will need amending.

What Happens in the Year of a Year-End Change?

A year-end change creates a stub period, and a stub period is where most of the lasting damage is done. Suppose a UK company with a 31 March year end shortens to 31 December to align with its US owner. It files form AA01, and the UK side produces a nine month accounting reference period running 1 April 2026 to 31 December 2026. A nine month corporation tax accounting period is unproblematic, because shorter than twelve months is allowed. The US side is where the work is.

If the foreign corporation's US tax year is genuinely changing, that is a change of annual accounting period, not merely a change of UK filing habit. The Instructions for Form 1128 explain that the required short period return covers the period that begins on the day following the close of the old tax year and ends on the day before the first day of the new tax year, and that a Form 1128 filed by a controlling domestic shareholder on behalf of a controlled foreign corporation is due no later than the due date, including extensions, of that shareholder's income tax return for its tax year with or within which ends the first effective year of the foreign corporation. The first effective year in a change of year is the short period itself.

Now apply the ends with or within rule to the change year and watch what happens. The twelve month period ending 31 March 2026 ends within calendar 2026. The nine month stub period ending 31 December 2026 ends with calendar 2026. Both periods end with or within the same shareholder year, and Regulations section 1.6038-2(e) is explicit about the consequence: if more than one annual accounting period ends with or within the United States person's taxable year, separate annual information returns must be submitted for each annual accounting period. So two separate Forms 5471 attach to the single 2026 Form 1040, each with its own dates below the title, its own schedules and its own exchange rates. Twenty-one months of UK corporate results land on one US return. Any subpart F or GILTI inclusion from both periods is bunched into 2026, which can move the shareholder's marginal rate, distort the foreign tax credit limitation for that year, and leave 2027 looking artificially light by comparison. Clients are rarely warned about this before they instruct the change, and the alignment they asked for is usually still the right long-term answer, but it should be a decision taken with the bunching in view.

Confirm first whether the US tax year is actually changing, or whether section 898 already required the calendar year and only the UK filing date is moving.
File two Forms 5471 for the change year where two annual accounting periods end with or within the same filer year, rather than merging them into one 21 month return.
Keep the same reference ID number on both. The instructions describe its purpose as uniquely identifying the foreign corporation in order to keep track of it from tax year to tax year, and inventing a second number for a stub breaks precisely the continuity the number exists to provide.
Complete item C separately for each period, because the percentage is measured at the end of each annual accounting period.
Check whether item D, the final Form 5471 checkbox, is being confused with a period change. A stub period is not a final year, and checking item D also pulls in Schedule O.
Re-derive the section 956 quarterly measurements for the stub, because the quarters of a nine month period are not the quarters of a twelve month year.
Expect the UK tax figures for the stub to be provisional until the corporation tax return for that shorter accounting period is actually filed.

Earnings and Profits and PTEP Through a Period Change

Earnings and profits is a cumulative pool, and the schedules that carry it are built to roll forward from one annual accounting period to the next. Schedule H computes current earnings and profits for the period. Schedule J carries the balances. When a stub period is inserted, the closing balance of the twelve month period must become the opening balance of the stub, and the closing balance of the stub must become the opening balance of the first full calendar year. If the stub is skipped, or if its figures are folded into one of the adjacent periods, the roll-forward breaks at a specific, identifiable year and stays broken in every later return until someone rebuilds it.

Previously taxed earnings and profits is less forgiving still, because Schedule P tracks it by year and by section 959 category. An inclusion that was reported on the 2026 Form 1040 has to appear as previously taxed earnings and profits attributable to a specific annual accounting period, and a distribution made later has to be matched against the right layer. Where a stub period has been mis-cut, the practical symptom is that a distribution years afterwards cannot be sourced cleanly to previously taxed earnings and profits, and what should be a tax-free return of already-taxed income starts to look like a taxable dividend. That is a real cash consequence arising from nothing more than a date, which is why we rebuild the period chain from incorporation whenever we take on a UK company whose year end has moved.

How Subpart F and GILTI Inclusions Land in the Shareholder's Year

The inclusion follows the same mapping as the form. A US shareholder takes into account its pro rata share of the foreign corporation's relevant income for the foreign corporation's tax year that ends with or within the shareholder's tax year. The Instructions for Form 8992 say the same thing for the GILTI computation, describing the shareholder as reporting its pro rata share of amounts for each controlled foreign corporation the tax year of which ends with or within the US shareholder's tax year, drawn from each corporation's Schedule I-1 of Form 5471. The Instructions for Form 5471 (Rev. December 2025) reflect current law by using the term net CFC tested income alongside GILTI following the 2025 legislation.

Two consequences follow for a non-calendar UK company. First, an inclusion is never apportioned across two Form 1040 years to reflect where the months fell. It lands whole in the single shareholder year in which the corporation's period closed. Second, a change of year end can therefore double up inclusions in one shareholder year and leave a neighbouring year with none, purely as a function of period closing dates. Schedule M reinforces the same logic for related party transactions: the instructions require a Category 4 filer to report the transactions that occurred during the foreign corporation's annual accounting period ending with or within the US person's tax year.

Translating a Non-Calendar Period Into US Dollars

A non-calendar period does not change the translation method, but it does change the inputs, and this is where a period error quietly becomes a currency error. The average rate that belongs on a Form 5471 for a period running 1 April 2025 to 31 March 2026 is the average over those twelve months. It is not the average for calendar 2025 and it is not the average for calendar 2026. Using a published calendar-year average because that is what the software offers will produce figures that are wrong by however much sterling moved, and the error compounds through earnings and profits because each year's mistake is added to a cumulative pool rather than washing out.

The Form 5471 instructions are specific about which rate belongs where. Schedule C reports in the foreign corporation's functional currency in accordance with US GAAP and translates using US GAAP translation principles. Schedule F reports in US dollars, with the balance sheet generally prepared in functional currency and translated using US GAAP translation rules. Schedule E translates foreign taxes at the average exchange rate for the tax year to which the tax relates under section 986(a). Schedule M translates at the average exchange rate for the foreign corporation's tax year under section 989(b). Worksheet B, by contrast, translates the section 956 amount at the year-end spot rate as provided in section 989(b), which for a 31 March period means the rate at 31 March and not at 31 December.

One formatting requirement catches people out regardless of period. The instructions require every exchange rate on Form 5471 to be reported using a divide-by convention, rounded to at least four places, meaning the number of units of foreign currency that equal one US dollar, and expressly not the number of US dollars that equal one unit of foreign currency. For sterling that is counter-intuitive, because the rate most people quote and most sources publish runs the other way. The instructions add that you must round to more than four places where failure to do so would materially distort the rate or the dollar equivalent.

Use the average rate for the foreign corporation's own period, cut to its actual opening and closing dates, not a calendar-year average.
In a stub year, compute a separate average for the stub. A nine month period has its own average, and reusing the twelve month figure understates or overstates every translated line.
Use the year-end spot rate where the instructions call for it, measured at the period end that actually applies, such as 31 March rather than 31 December.
Report every rate as units of sterling per one US dollar, to at least four decimal places, and to more where four would materially distort the result.
Keep the rate source and the date range in the file, because in a period-change year you will be defending two different rates for two Forms 5471 attached to the same Form 1040.

Reference ID Numbers and the Schedules a Period Change Touches

Most UK companies owned by US individuals have no US employer identification number, so the reference ID number does the identifying work. The instructions require one in item 1b(2) where no EIN was entered in item 1b(1), though a filer may enter both. It must be alphanumeric with no special characters and no spaces, is limited to 50 characters, and the same number must be used consistently from tax year to tax year for a given foreign corporation. If a number changes, the new number goes in item 1b(2) and the previous number or numbers in item 1b(3), a correlation required only in the first year the new number is used. Where the shareholder also files Schedule A or Schedule B of Form 8992, the reference ID number used there must match the one on Form 5471.

As to which schedules a period question affects, the honest answer is nearly all of them, because almost every schedule reports for the annual accounting period. Schedules C, E, F, G, H, I-1, J, M, P, Q and R all take their figures from the corporation's period. The instructive exception is Schedule O. The instructions state that except for information contained on Schedule O, you report information for the tax year of the foreign corporation that ends with or within your tax year, and that when filing Schedule O you report acquisitions, dispositions, and organizations or reorganizations that occurred during your tax year. So in a year where a share transaction and a year-end change happen together, Schedule O is cut to the filer's calendar year while everything around it is cut to the corporation's period. That single exception is worth flagging on the workpaper, because it is easy to align Schedule O to the corporation's period out of consistency and be wrong for that reason alone.

Filer status is measured on a different clock again, and this catches people who assume everything on the form runs on one calendar. The instructions define control for Category 4 purposes as owning, at any time during that person's tax year, stock possessing more than 50 percent of the total combined voting power of all classes of stock entitled to vote, or more than 50 percent of the total value of shares of all classes of stock. Note the reference point: it is the filer's tax year, not the foreign corporation's annual accounting period. So whether you are a Category 4 filer at all is tested across your calendar year, while what you then report is cut to the company's period. On a 31 March company whose shares changed hands during the year, those two windows can give different answers, and both have to be worked through rather than assumed to agree.

When the UK Accounts Are Not Ready Before the US Deadline

A non-calendar year end creates a scheduling problem that has nothing to do with the law and everything to do with practice, and it is the reason these returns go on extension as a matter of routine rather than as a matter of crisis. A private UK company has nine months from its accounting reference date to deliver accounts to Companies House. A company with a 31 March 2026 year end therefore has until 31 December 2026, and in the real world a good many sets of accounts are finalised in November or December. The US shareholder, meanwhile, needs those figures for the 2026 Form 1040, whose automatic extended deadline for a taxpayer abroad is 15 June 2027. So in that particular pairing the timetable works comfortably.

Reverse the order and it does not. A 30 September 2026 year end also lands on the 2026 Form 1040, but the UK accounts for it are not due at Companies House until 30 June 2027, two weeks after the US extended deadline of 15 June 2027. The IRS position is that US citizens and resident aliens abroad get an automatic two-month extension to 15 June without requesting one, and can then request a further extension to 15 October by filing Form 4868 before that automatic extension date, but interest still runs on any tax not paid by the regular April due date. The practical answer is to agree a US reporting timetable with the UK accountant that is driven by the Form 1040 calendar rather than by the Companies House calendar, and to extend deliberately rather than file a Form 5471 built on figures that will be superseded.

The same mismatch runs through the foreign tax credit. UK corporation tax is computed for an accounting period that cannot exceed twelve months and is payable nine months and one day after the end of that period for a company with taxable profits up to 1.5 million pounds, with instalments above that. The US inclusion, by contrast, attaches to the shareholder year in which the corporation's period closed. Where a UK period straddles two calendar years, the tax that economically relates to the reported income may be assessed, and paid, on a different rhythm from the year in which the income is included. That is a credit timing question rather than a credit entitlement question, but it has to be tracked deliberately, and it is another reason the period chain needs to be documented rather than reconstructed each year from memory.

Penalties Are Measured Per Annual Accounting Period

The penalty structure reinforces why periods matter rather than being an administrative nicety. The instructions state that a 10,000 dollar penalty is imposed for each annual accounting period of each foreign corporation for failure to furnish the information required by section 6038(a) within the time prescribed. If the information is not filed within 90 days after the IRS has mailed a notice of the failure, an additional 10,000 dollar penalty per foreign corporation is charged for each 30-day period or fraction of one during which the failure continues after the 90-day period, limited to a maximum of 50,000 dollars for each failure. Separately, a failure to file or report all required information within the time prescribed brings a 10 percent reduction of the foreign taxes available for credit under sections 901 and 960, with a further 5 percent reduction for each three month period or fraction of one during which the failure continues more than 90 days after notice.

Read the unit of measurement carefully. The exposure is per annual accounting period, not per year of the shareholder's life and not per Form 1040. A change-of-year-end that produces two periods in one filer year produces two potential penalties in that filer year. A stub period that was never reported at all is a standalone failure, whatever was done with the periods either side of it.

How We Handle a Non-Calendar UK Year End

The method is unglamorous and it is the reason these files come out clean. We do not start from the UK accounts. We start from the ownership position, settle the required year question under section 898, and only then decide which twelve months the return is going to describe.

Pull the company's full Companies House filing history and list every accounting reference period since incorporation, including any shortened or extended ones and any change made by form AA01.
Settle whether the company is a section 898 specified foreign corporation for each of those periods, since ownership can change and the answer is not necessarily the same throughout.
Build a mapping table of foreign corporation period against Form 1040 year on the ends with or within rule, and identify every filer year that picks up two periods or none.
Reconcile that table to the Forms 5471 actually filed, if any, and mark every period that was reported on the wrong return, reported twice or never reported.
Rebuild the Schedule J earnings and profits and Schedule P previously taxed earnings and profits roll-forward across the corrected period chain before touching the current year.
Set the average and year-end rates for each period from its own opening and closing dates, expressed as sterling per one US dollar to at least four decimal places.
Fix the reference ID number and keep it constant, correlating any previous numbers in item 1b(3) in the first year a new one is used.
Where periods were missed, scope the remediation route on its facts, whether that is the Streamlined Foreign Offshore Procedures with three years of returns, six years of FBARs and a Form 14653, or another route entirely.

A non-calendar accounting period is not a defect in a UK company, and there is rarely any UK reason to move a well-established 31 March or 30 September year end. What it demands is that the US preparer stop treating the statutory accounts as the starting point and treat them as one input into a period question that US law has already answered. Get the period right and the schedules follow. Get it wrong and every schedule is internally consistent, beautifully presented, and describing the wrong twelve months.