Does the UK Personal Savings Allowance reduce my US tax on savings interest?

No. The Personal Savings Allowance is a UK Income Tax relief of £1,000 for basic rate taxpayers, £500 for higher rate taxpayers and £0 for additional rate taxpayers. The United States has no equivalent. A US citizen reports all UK interest on Schedule B of Form 1040, and any interest the allowance shelters from UK tax carries no UK tax to claim as a foreign tax credit.

Is cash ISA interest taxable in the US for an American living in the UK?

Yes. A cash ISA is tax-free for UK purposes, but the US does not recognise the wrapper. The interest is reported on Schedule B in dollars for the calendar year it is credited, and the account is reported on the FBAR and, where thresholds are met, Form 8938. Because the UK charges no tax on ISA interest, there is no UK tax on that income to credit.

When do I have to register for Self Assessment because of UK savings interest?

GOV.UK says that if your savings interest is more than £10,000 you need to report it on a Self Assessment tax return, and HMRC will send a notice to file if your bank reports interest above that level. If you have not filed before, you must tell HMRC by 5 October following the end of the tax year. Below £10,000, HMRC usually collects the tax through your tax code.

Can I use UK tax on savings interest to offset the US Net Investment Income Tax?

Not on the face of the forms. The Net Investment Income Tax is a 3.8% charge on interest and other investment income above $200,000 of modified adjusted gross income for single filers, $250,000 for joint filers and $125,000 for married filing separately. The Form 1116 instructions state that the regular tax liability used for the foreign tax credit excludes it. Treaty-based claims exist but are disputed positions.

Which exchange rate do I use to report UK interest on Schedule B?

The IRS says the general rule is the spot rate when the item is received, and that it has no official rate but generally accepts any posted exchange rate used consistently. It also publishes yearly average rates. For interest credited steadily through the year, the yearly average is commonly used; for a single large payment, the rate on the payment date is a closer fit. The method should be applied consistently.

How is interest on a joint account with my non-US spouse taxed in the UK and the US?

HMRC splits interest on a joint account equally between the holders unless told it should be divided differently, and each holder applies their own tax band and allowances. For US purposes, a spouse who is not a US citizen or resident is generally outside US tax on UK interest unless a joint return election is made. The US citizen still reports the joint account on the FBAR.

US UK Tax Returns Preparation: UK Savings Allowance

US UK tax returns preparation for savings interest starts from one uncomfortable fact: the UK Personal Savings Allowance, the starting rate for savings and the ISA wrapper exist only on the UK side, while the US return taxes every pound of UK interest from the first pound. A US citizen living in the UK therefore reports the same interest twice, under two sets of rules, in two currencies and across two different tax years. Where the UK charges tax, a foreign tax credit normally removes the US income tax on that interest. Where the UK charges nothing, there is nothing to credit and the US tax on that slice is simply payable.

For most of the clients whose returns we prepare, the headline allowance is not the issue, because additional rate taxpayers receive no Personal Savings Allowance at all. The real exposure sits in cash ISA interest, Premium Bond prizes, years in which UK income dips, deposits held by a spouse, the 3.8% Net Investment Income Tax and a timing gap between the UK tax paid and the US year in which the interest is taxed.

What is the UK Personal Savings Allowance and who actually receives it?

The Personal Savings Allowance is the amount of savings interest a UK taxpayer can receive in a tax year without paying Income Tax on it, and its size depends on the taxpayer's Income Tax band. GOV.UK sets out the figures at https://www.gov.uk/apply-tax-free-interest-on-savings/how-much-is-tax-free and they are unchanged for the tax year running from 6 April 2026 to 5 April 2027.

Basic rate taxpayers: a Personal Savings Allowance of £1,000.
Higher rate taxpayers: a Personal Savings Allowance of £500.
Additional rate taxpayers: a Personal Savings Allowance of £0.
Starting rate for savings: up to £5,000 of interest free of tax, but only where other taxable income (excluding savings interest and dividends) is below £17,570. Every £1 of other income above the Personal Allowance reduces it by £1.
Personal Allowance: if wages, pension or other income do not use it up, HMRC applies the unused part to savings interest.

Two points matter for wealthy savers. First, GOV.UK says that to work out your band you add all the interest you have earned to your other income, so a banker with a salary just under the additional rate threshold can be pushed over it by the interest itself and lose the £500 allowance. Second, the bands at https://www.gov.uk/income-tax-rates for 2026 to 2027 put the higher rate at 40% on taxable income from £50,271 to £125,140 and the additional rate at 45% above £125,140, with the Personal Allowance reduced to zero once income reaches £125,140. An additional rate taxpayer has no Personal Allowance, no starting rate for savings and no Personal Savings Allowance: every pound of interest outside an ISA is taxed at 45%.

The allowance itself therefore matters in three situations: a higher rate year (the £500), a low-income year such as a career break or a year of arrival (when the starting rate and the full £1,000 can both apply), and a spouse or partner with modest income who holds part of the family's cash.

How do UK banks pay interest and how does HMRC collect the tax?

UK banks and building societies pay interest without deducting tax and report it to HMRC afterwards. The overview at https://www.gov.uk/apply-tax-free-interest-on-savings explains that after 5 April each year the bank or building society tells HMRC about the interest paid for the previous year, and that HMRC adds together the interest from all of a person's accounts. What happens next depends on the amount, as set out at https://www.gov.uk/apply-tax-free-interest-on-savings/how-you-pay-tax-on-savings-interest in the same guide.

Where savings interest is £10,000 or less and the saver is employed or receives a pension, HMRC sends a tax calculation and will usually collect the tax through the tax code, which may also be changed to include an estimate of the current year's interest. Where there is no tax code to adjust, HMRC may issue a Simple Assessment letter. Anyone already inside Self Assessment reports the interest on the return.

Where savings interest is more than £10,000, the GOV.UK wording is direct: you need to tell HMRC how much interest you earned on a Self Assessment tax return, and if the bank reports more than £10,000 of interest HMRC will send a notice to file. Someone not already in Self Assessment must register. The deadline page at https://www.gov.uk/self-assessment-tax-returns/deadlines confirms that a person who needs to complete a return for the previous year, and has not sent one before, must tell HMRC by 5 October. For interest earned in the tax year that ended on 5 April 2026, that means 5 October 2026, with the online return and the tax due by 31 January 2027.

For a reader with seven-figure deposits, the £10,000 line is crossed quickly. UK tax on interest is not withheld at source: it is paid months later, which creates the timing problem discussed below.

Are UK tax rates on savings income changing in April 2027?

Yes. The government announced on 26 November 2025 that tax on savings income will rise by 2 percentage points across all bands from April 2027. The policy paper at https://www.gov.uk/government/publications/changes-to-tax-rates-for-property-savings-dividend-income/changes-to-tax-rates-for-property-savings-dividend-income states that the basic rate on savings will move from 20% to 22%, the higher rate from 40% to 42% and the additional rate from 45% to 47%, and describes the £1,000 and £500 allowances and the £5,000 starting rate as remaining available.

For a US citizen the change cuts one way only. A higher UK rate produces more creditable UK tax on interest that was already fully covered, and does nothing for interest the UK does not tax or for the Net Investment Income Tax.

How does US UK tax returns preparation handle the same interest on Form 1040?

On the US return, all UK interest is ordinary taxable income, reported on Schedule B of Form 1040 in US dollars for the calendar year in which it is credited. There is no US equivalent of the Personal Savings Allowance, no starting rate for savings and no recognition of the ISA wrapper. The Schedule B instructions at https://www.irs.gov/instructions/i1040sb require the schedule where taxable interest exceeds $1,500, and separately where the filer had a foreign financial account, which describes every reader of this article.

Schedule B Part I: each UK bank, building society and National Savings account listed by payer with the dollar amount of interest, including interest within a UK allowance or inside a cash ISA.
Schedule B Part III, line 7a: whether you had a financial interest in or signature authority over a foreign financial account, and whether you must file FinCEN Form 114.
Schedule B Part III, line 7b: the country or countries where the accounts are held, if an FBAR is required.
Form 1116: the foreign tax credit for UK Income Tax paid or accrued on the interest.
Form 8960: the Net Investment Income Tax, where income is above the threshold.
Form 8938: specified foreign financial assets, where the reporting threshold is met.

Conversion to dollars is a method choice. The IRS page at https://www.irs.gov/individuals/international-taxpayers/yearly-average-currency-exchange-rates says that in general the rate to use is the spot rate prevailing when the item is received, that the IRS has no official exchange rate and that it generally accepts any posted exchange rate that is used consistently. It also publishes yearly average rates, which suit interest credited evenly through the year. A single large payment, such as a fixed-term deposit maturing in one lump, is a better fit for the rate on the date of payment.

Cash ISA interest is the cleanest example of the mismatch. GOV.UK confirms at https://www.gov.uk/individual-savings-accounts that ISAs are tax-free in the UK, with a subscription limit of £20,000 for 2026 to 2027, yet the interest goes on Schedule B like any other bank interest. Premium Bond prizes follow the same pattern: GOV.UK lists premium bond wins among tax-free income at https://www.gov.uk/income-tax while the US taxes prizes as ordinary income. Fixed-term deposits longer than a year that pay all their interest at maturity also deserve a check, because the US year of taxation is not always the year of payment.

Why does the allowance create a UK tax-free but US-taxable slice with no credit?

A foreign tax credit is a credit for foreign income tax actually paid or accrued, not for tax that a foreign country chose not to charge. Where the Personal Savings Allowance, the starting rate for savings, an unused Personal Allowance, an ISA or the Premium Bond exemption reduces the UK tax on a slice of interest to nil, that slice arrives on Form 1040 fully taxable with no UK tax attached to it.

Interest is generally passive category income, with its own Form 1116 and its own limitation. The instructions at https://www.irs.gov/instructions/i1116 state that passive income does not include high-taxed income, meaning income on which the foreign taxes paid, after allocation of expenses, exceed the highest US tax that can be imposed on it. They refer to Regulations section 1.904-4(c) for the detail, under which income that bore no foreign tax is tested separately from income that did. UK interest taxed at the additional rate can therefore be reclassified out of the passive category, taking its UK tax with it, with the entry marked HTKO on the form. What remains is the untaxed interest, with no UK tax beside it.

The surplus UK tax on taxed interest moves to a category where a UK-resident filer usually has surplus credits already, and the ISA interest, the Premium Bond prizes and any interest sheltered by a UK allowance stay behind as US-taxable income with no credit. Whether the high-tax rule applies depends on the actual UK rate, the expenses allocated to the income and the US rate in force, so it is tested on the figures each year.

How does the UK tax year mismatch distort the foreign tax credit?

The UK tax year runs from 6 April to 5 April, while the US tax year for an individual is the calendar year. Interest credited between 1 January and 5 April belongs to one UK tax year and interest credited from 6 April to 31 December belongs to the next, yet both sit on the same Form 1040. The UK tax on them is computed on two UK returns and paid on different dates.

IRS Publication 514 at https://www.irs.gov/publications/p514 explains the two ways of claiming the credit. A cash method taxpayer claims it in the year the foreign tax is paid, or can choose to take it in the year the taxes accrue, and the publication says foreign taxes generally accrue on the last day of the foreign tax year for which the foreign return is filed. For a UK resident that day is 5 April.

Neither method lines the tax up with the income. On the paid basis, UK tax on interest is often settled a year or more after the interest was credited. On the accrual basis, the UK tax credited on a calendar 2026 US return is the tax for the UK year ended 5 April 2026, roughly three quarters of which relates to interest earned in calendar 2025. While balances and interest rates are stable the two streams roughly offset. They stop offsetting in exactly the years that matter:

A liquidity event, bonus or property sale that puts a large balance on deposit part-way through a calendar year.
A sharp move in interest rates, so that one UK year's tax is much higher or lower than the next.
The year of arrival in or departure from the UK, when one side has a full year and the other a part year.
The April 2027 rate rise, which increases the UK tax on interest from one UK year to the next within a single US year.

In those years the US return can show substantial interest with too little UK tax to credit against it, followed by a year with the opposite problem. The Form 1116 instructions allow unused foreign tax to be carried back one year and forward ten years within the same category, which normally repairs the position, but a carryback means an amended return and in the meantime the US tax is payable. The failure mode we see most often is a return that pairs calendar year interest with the tax shown on a UK return for a different period.

Does the Net Investment Income Tax apply to UK savings interest?

Yes. The IRS confirms at https://www.irs.gov/individuals/net-investment-income-tax that the Net Investment Income Tax is a 3.8% tax, that net investment income includes interest, and that it applies where modified adjusted gross income exceeds $250,000 for married filing jointly, $125,000 for married filing separately and $200,000 for single or head of household filers. The thresholds are not indexed for inflation, and the tax is computed on Form 8960. A US citizen married to a non-US spouse and filing separately reaches $125,000 very quickly.

The foreign tax credit position against this tax needs care. The Form 1116 instructions state that the regular tax liability against which the credit is figured does not include the section 1411 net investment income tax. On the face of the forms, therefore, UK Income Tax at 45% on interest does not reduce the 3.8% charge on the same interest. Whether the US-UK treaty requires a credit is a question on which taxpayers have taken treaty-based positions and which has been disputed. We treat any such claim as a disclosed position to be weighed on its merits, not a routine entry.

What does this look like in a worked illustration?

The following is an illustration only, using assumed figures, an assumed interest rate and an assumed exchange rate of $1.30 to £1, which is not the IRS yearly average for any year. Assume a single US citizen, resident in London, with employment income well above the additional rate threshold. During calendar 2026 she holds £1,500,000 in UK savings accounts in her sole name earning an assumed 4%, a cash ISA of £100,000 earning the same rate, and Premium Bonds that pay £1,200 in prizes.

On the UK side, the savings accounts produce £60,000 of interest. Her Personal Savings Allowance is £0 and the interest is taxed at 45%, giving UK tax of £27,000 across the two UK tax years that the calendar year straddles. The £4,000 of ISA interest and the £1,200 of prizes bear no UK tax.

On the US side, Schedule B shows £64,000 of interest, which is $83,200 at the assumed rate, and the prizes add $1,560 of other income. The UK tax-free items total £5,200, or $6,760. If the taxed interest is reclassified under the high-tax rule, that $6,760 has no credit against it, and at an assumed 37% US marginal rate the income tax on it is about $2,500. The Net Investment Income Tax at 3.8% on $83,200 adds about $3,160, assuming her modified adjusted gross income exceeds the $200,000 threshold by at least that much. The US cash cost in this illustration is roughly $5,660, on savings for which she has already paid £27,000 to HMRC.

Now change one fact. Suppose £1,000,000 of the deposit arrived in July 2026 from the sale of a business interest. On an accrual basis, the UK tax available on her 2026 US return is the tax for the UK year ended 5 April 2026, when the balance was only £500,000. The shortfall is recovered only when the following year's surplus is carried back.

Which savings accounts go on the FBAR and Form 8938?

Every UK savings account, cash ISA and fixed-term deposit is a foreign financial account for FBAR purposes. The IRS page at https://www.irs.gov/businesses/small-businesses-self-employed/report-of-foreign-bank-and-financial-accounts-fbar confirms that the report is due on 15 April following the calendar year, with an automatic extension to 15 October, and that the maximum value of each account must be recorded. The requirement arises where the aggregate value of foreign financial accounts exceeds $10,000 at any time during the year, and the report is filed through FinCEN's BSA E-Filing System, separately from the tax return.

Form 8938 is filed with the return and has higher thresholds. The IRS comparison at https://www.irs.gov/businesses/comparison-of-form-8938-and-fbar-requirements gives the figures for taxpayers living abroad: specified foreign financial assets of more than $200,000 on the last day of the tax year or more than $300,000 at any time for single filers and those married filing separately, and more than $400,000 or $600,000 respectively for married couples filing jointly. A reader with substantial deposits files both forms, and the accounts listed should agree with Schedule B.

What does Article 11 of the US-UK treaty do, and what does the saving clause take away?

Article 11 of the US-UK income tax convention provides that interest arising in one country and beneficially owned by a resident of the other is taxable only in that other country. The text is published by the US Treasury at https://home.treasury.gov/system/files/131/Treaty-UK-7-24-2001.pdf and read in isolation it suggests that a UK resident's interest is a matter for the UK alone.

The saving clause removes that comfort for US citizens. Article 1, paragraph 4 says that a country may tax its residents, and by reason of citizenship may tax its citizens, as if the convention had not come into effect, and Article 11 is not among the exceptions listed in paragraph 5. The United States therefore taxes a citizen's UK interest in full.

What does survive the saving clause is Article 24, the relief from double taxation article, which paragraph 5 expressly preserves. For interest paid by UK banks the relief is the ordinary US foreign tax credit for UK tax. For interest from US accounts held by a US citizen who is UK resident, paragraph 6 of Article 24 sets a different order: the United States allows a credit for the UK tax and the income is treated as arising in the UK to the extent necessary to avoid double taxation. The Form 1116 instructions put treaty re-sourced income in its own category, so clients with deposits on both sides of the Atlantic often need more than one Form 1116 for interest alone.

How are joint accounts with a non-US spouse handled on each return?

The UK default is simple. GOV.UK states that for a joint account HMRC will split the interest equally between the account holders, who should contact HMRC if they think it should be split differently. Each spouse then applies their own band and allowances to their half, so a non-US spouse on the basic or higher rate has a Personal Savings Allowance that the additional rate spouse does not.

The US position follows ownership. A spouse who is neither a US citizen nor a US resident is generally not taxed by the United States on UK bank interest unless the couple has elected to file a joint US return. Where the US citizen files as married filing separately, the citizen reports the interest that belongs to them, and the two returns should tell the same story about who owns the money.

Information reporting is less forgiving than the income split. A US person with a financial interest in a jointly held account reports that account on the FBAR, and the IRS exception that lets one spouse file for both relies on FinCEN Form 114a and on the couple jointly owning all their foreign accounts.

What should be on file before the two returns are prepared?

Interest certificates or statements for every UK account, split at 5 April so that the calendar year figure and both UK tax year figures can be derived.
Cash ISA interest and Premium Bond prize records, which do not appear on the UK return but belong on the US return.
The UK tax calculation, tax code notices and Self Assessment payment dates showing how and when the tax on interest was collected.
Confirmation of whether an accrual election for foreign taxes has been made in an earlier US year.
Maximum and year-end balances for every account, for the FBAR and Form 8938.
Ownership details for joint accounts and the tax status of the other holder.

With those records a preparer or specialist can reconcile Schedule B to the UK return, place the UK tax in the correct US year and identify the slice on which US tax is payable.