Does the IRS have six years or unlimited time for missed US tax returns?

If no return was filed for a year, section 6501(c)(3) lets the IRS assess tax at any time, because the three-year clock only starts when a valid return is filed. The six-year period in section 6501(e) applies only to returns that were filed but omitted substantial income. Separately, the IRS has an internal policy of normally pursuing no more than six years of delinquent returns, but that is administrative practice, not a statutory limit.

I reported my UK salary but left out ISA income. Is my return open for six years?

Possibly, even if the ISA income is small relative to your salary. Section 6501(e)(1)(A)(ii) applies a six-year period where more than $5,000 of omitted income is attributable to a specified foreign financial asset of the kind covered by section 6038D, and a UK-held ISA account is such an asset. No percentage test applies to that prong, so high earners can be caught without coming near 25 percent.

Does the $5,000 foreign-asset rule apply if I was below the Form 8938 threshold?

Yes. The statute says the asset qualifies if information about it would be reportable under section 6038D if that section were applied without regard to its dollar threshold and without regard to exceptions made under section 6038D(h)(1). So being under the Form 8938 filing threshold does not prevent the six-year period applying where more than $5,000 of income from a UK account was omitted.

How is gross income measured for the 25 percent test?

The test compares omitted gross income with the gross income stated on the return, not adjusted gross income or taxable income. For a trade or business, gross income means gross receipts from selling goods or services before cost of sales. An overstated basis counts as an omission, adequately disclosed items are excluded, and, following Toso v. Commissioner, only the current-year portion of a PFIC excess distribution is counted.

Does the IRS six-year rule have anything to do with HMRC's time limits?

No. Section 6501(e) is a US federal rule and HMRC applies its own separate time limits for UK assessments, which lengthen where an error was careless or deliberate. The two systems do not align, and much of the income that triggers the US rule, such as ISA interest, dividends and gains, is exempt in the UK and never appears on a Self Assessment return, so HMRC is unlikely to be the source of any US discovery.

Is the FBAR penalty period the same as the six-year tax assessment period?

No. The FBAR penalty period comes from 31 USC 5321(b)(1), which allows a civil penalty to be assessed within six years beginning on the date of the transaction concerned, generally measured from the FBAR due date. It runs independently for each year and does not depend on any income omission. The tax assessment period under section 6501(e) depends on the size and source of income left off a filed return.

Missed US Tax Returns: The 6501(e) Six-Year Rule

Missed US tax returns and incomplete US tax returns are treated very differently by the assessment statute: if you never filed, the IRS clock never starts, but if you filed and left income off, the normal three-year window becomes six years under section 6501(e) of the Internal Revenue Code when the omission is large enough. For a UK-resident American, large enough means either more than 25 percent of the gross income stated on the return, or more than $5,000 of omitted income attributable to a foreign financial asset of the kind reported under section 6038D. That second test is the one high earners in London routinely trip, because it has nothing to do with percentages.

This article is about section 6501(e) itself: what the statute actually says, how the IRS measures gross income for the 25 percent test, where the adequate-disclosure rule helps and where it does not, how the six-year period sits next to the unlimited periods for no return, fraud and missing information returns, and how all of that shapes the choice between simple amended returns, the Streamlined Foreign Offshore Procedures and a full catch-up filing. In the returns we prepare for UK-based bankers, fund professionals, business owners and investors, the most common starting point is not a person who never filed. It is a person who filed every year, reported the salary, and left out the ISA, the UK fund gains, the flat that is let out, or part of a bonus that was paid through a different payroll.

What is the section 6501(e) six-year assessment period?

The section 6501(e) six-year assessment period is a statutory extension of the IRS's time to assess income tax on a filed return, from three years to six years after the return was filed, where the taxpayer omitted a substantial amount of gross income. The statute is published at https://www.law.cornell.edu/uscode/text/26/6501 and the starting point is section 6501(a): tax must generally be assessed within three years after the return was filed. Section 6501(e)(1)(A) then provides that if the taxpayer omits from gross income an amount properly includible in it, and that amount either exceeds 25 percent of the gross income stated in the return, or is attributable to assets reportable under section 6038D and exceeds $5,000, the tax may be assessed at any time within six years after the return was filed.

Two features matter immediately. First, the six-year period is not limited to the omitted item. The IRS's own training material on the statute of limitations, the international practice unit at https://www.irs.gov/pub/fatca/int_practice_units/int_c_115r.pdf, states that where the omission exceeds 25 percent, the six-year period applies to the entire return, not just the omitted income. Second, section 6501(e) only operates where a return was filed. If there is no return, a different and far wider rule applies, which we come to below.

How does the 25 percent test work for missed US tax returns income?

The 25 percent prong, section 6501(e)(1)(A)(i), compares two numbers: the gross income omitted from the return, and the gross income stated in the return. The IRS practice unit expresses it as a simple fraction, gross income omitted divided by total gross income reported. If the result is above 25 percent, the six-year period applies. The comparison is to gross income, not adjusted gross income and not taxable income, which is why deductions, the foreign tax credit and the standard deduction are irrelevant to the test even though they may reduce the tax actually due to nil.

Section 6501(e)(1)(B) sets out how gross income is measured for this purpose. The points that matter most for UK-based filers are these:

Trade or business income is measured at the top line. For a trade or business, gross income means the total amounts received or accrued from the sale of goods or services, before reduction for the cost of those sales or services. A UK consultant or sole trader who reported only net profit is compared on gross receipts, which makes the denominator larger and a given omission less likely to cross 25 percent.
Overstated basis counts as an omission. Section 6501(e)(1)(B)(ii) treats an understatement of gross income caused by an overstatement of unrecovered cost or other basis as an omission. The IRS practice unit explains that this was added in 2015 to reverse the Supreme Court's Home Concrete decision. Inflating the cost of UK shares or a UK property on sale therefore counts.
Adequately disclosed amounts are excluded. Section 6501(e)(1)(B)(iii) says an amount omitted from gross income is not taken into account if it is disclosed in the return, or in a statement attached to it, in a manner adequate to apprise the IRS of the nature and amount of the item. This does not apply to overstated-basis cases.
Only current-year PFIC gain is gross income. The practice unit cites Toso v. Commissioner, 151 T.C. No. 4 (2018): current-year PFIC gains are included in gross income for the 25 percent test, but the portion of an excess distribution allocated to earlier years is not, because section 1291 excludes it from gross income.

That last point is a genuine technical gap in most published guidance on missed US tax returns. Many UK-resident Americans hold UK authorised funds such as OEICs inside a stocks and shares ISA or a general investment account, and those funds are typically passive foreign investment companies for US purposes. When the omitted income is a PFIC gain taxed under the excess distribution regime, only the slice allocated to the current year counts toward the 25 percent numerator. The same gain can therefore look much smaller for statute purposes than it does for tax-computation purposes.

What is the $5,000 foreign financial asset prong?

The second prong, section 6501(e)(1)(A)(ii), was added by the Hiring Incentives to Restore Employment Act of 2010, the same legislation that introduced FATCA and Form 8938. It extends the period to six years where the omitted amount is attributable to one or more assets with respect to which information is required to be reported under section 6038D, and the omitted amount is more than $5,000. There is no percentage test at all.

The statutory wording goes further than most summaries acknowledge. The asset qualifies if information about it is required to be reported under section 6038D, or would be so required if section 6038D were applied without regard to its dollar threshold and without regard to exceptions provided under section 6038D(h)(1). In plain terms, it does not matter that your foreign assets were below the Form 8938 filing threshold, and it does not matter that an asset was carved out of Form 8938 because it is reported on another form. If the asset is the kind of specified foreign financial asset that section 6038D covers, and more than $5,000 of income from it was left off the return, the six-year period applies. The IRS summary of FATCA reporting at https://www.irs.gov/businesses/corporations/summary-of-fatca-reporting-for-us-taxpayers explains which assets are specified foreign financial assets; a UK bank account, a UK brokerage account and an ISA held with a UK provider are the obvious examples.

On timing, the practice unit states that the effective date of this prong limits it to years for which section 6038D is effective, which for individuals means tax years beginning after 18 March 2010, generally 2011 onwards, and it cites Rafizadeh v. Commissioner, 150 T.C. 1 (2018). For any year a UK-resident American would realistically be dealing with today, the prong is live.

Does the adequate-disclosure exception protect the foreign-asset prong?

This is a question we are asked often, and the honest answer is that the statutory text does not carve the foreign-asset prong out of the disclosure rule. Section 6501(e)(1)(B) opens with the words for purposes of subparagraph (A), which covers both prongs, and the only express exclusion from the disclosure rule in clause (iii) is for overstatements of unrecovered cost or other basis. So, read on its face, an amount that is genuinely disclosed on the return, or in an attached statement, in a manner adequate to apprise the IRS of both its nature and its amount, is not counted as omitted under either prong.

The practical difficulty is the standard itself. The disclosure must tell the IRS what the item is and how much it is. Listing a UK account on Form 8938 with its maximum value tells the IRS the account exists; it does not by itself tell the IRS the amount of dividends or gains the account produced that were left off Schedule B or Schedule D. Whether a given disclosure is adequate is fact-specific, and we do not treat a bare Form 8938 or FBAR listing as a safe harbour. If an income item is uncertain, the protective course is to report it, or to attach a statement that states the item and its amount explicitly.

Worked illustration: when does a UK ISA omission cross 25 percent?

The following figures are an illustration only, not client data. We assume an exchange rate of 1 GBP = 1.25 USD throughout purely for arithmetic; in practice each year is converted using the rate appropriate to that year. Assume every item below is ordinary gross income, that is, cash interest, dividends on individual shares and gains on individual shares, not PFIC fund gains, so the Toso point does not reduce the numerator.

Filer A, a mid-career professional. UK salary of 160,000 GBP reported on the return, so gross income stated is 200,000 USD. Twenty-five percent of that is 50,000 USD, so the omission must exceed 50,000 USD. Omitted: gross rents from a let London flat of 24,000 GBP (30,000 USD) and gains on individual shares sold inside a stocks and shares ISA of 20,000 GBP (25,000 USD). Total omitted 55,000 USD, which is 27.5 percent. The 25 percent prong is crossed, and the six-year period applies to the whole return.
Filer A without the flat. Omit only the ISA gains of 25,000 USD against 200,000 USD stated. That is 12.5 percent, so the 25 percent prong is not crossed. But the ISA is held with a UK provider, the income is attributable to a specified foreign financial asset, and 25,000 USD exceeds 5,000 USD. The six-year period applies anyway, under the second prong.
Filer B, a senior banker. Salary and bonus of 960,000 GBP reported, so gross income stated is 1,200,000 USD and the 25 percent threshold is 300,000 USD. Omitted: interest and dividends from a UK cash ISA, a stocks and shares ISA holding individual shares, and a UK general investment account, totalling 32,000 GBP (40,000 USD). That is about 3.3 percent of stated gross income, nowhere near 25 percent. It is still more than 5,000 USD attributable to specified foreign financial assets, so the return stays open for six years.

Filer B is the pattern that catches high-net-worth filers. A high salary makes the 25 percent prong almost impossible to trigger through investment income alone, which gives a false sense of security. The $5,000 foreign-asset prong ignores the size of the salary entirely. In our experience, the higher the reported earnings, the more likely it is that the foreign-asset prong, not the percentage test, is the one that keeps a year open.

How does 6501(e) compare with no return, fraud and missing Forms 5471 or 8938?

Section 6501(e) is only one of several exceptions to the three-year rule, and for UK-resident Americans it rarely operates alone. The main comparisons are these:

No return filed, section 6501(c)(3). In the case of failure to file a return, tax may be assessed at any time. The practice unit explains that the clock does not start until a valid return is filed, and then runs for three years from filing. This is the position of anyone with genuinely missed US tax returns.
False or fraudulent return, section 6501(c)(1). Where a return is false or fraudulent with intent to evade tax, assessment may be made at any time. The six-year rule in 6501(e) is not a fraud rule; it applies to innocent omissions as well.
Missing international information returns, section 6501(c)(8). Where information required under sections including 6038 (Form 5471), 6038B (Form 926), 6038D (Form 8938) and 1298(f) (Form 8621 for PFICs) is not furnished, the time to assess tax with respect to the return to which the information relates does not expire before three years after the information is furnished. Under 6501(c)(8)(B), if the failure was due to reasonable cause and not wilful neglect, the extension applies only to the items related to the failure.
Constructive dividends, section 6501(e)(1)(C). Omitted section 951(a) inclusions from a controlled foreign corporation carry their own six-year period, which matters to owners of UK companies with Subpart F exposure.

The interaction is what makes cross-border cases different. A UK company owner who filed a Form 1040 but never filed Form 5471 does not have a six-year problem; under 6501(c)(8) the whole return can remain open until three years after the Form 5471 is finally furnished, narrowed to related items only if reasonable cause is shown. Similarly, a filer who left out ISA income and also had a Form 8621 obligation for ISA-held UK funds that was never met may find that 6501(c)(8), not 6501(e), is the controlling rule. Section 6501(e) sets a six-year ceiling; the (c) exceptions can remove the ceiling altogether.

Does filing an amended return restart or extend the clock?

Generally, no. The practice unit states that the filing of a taxable amended return does not, in general, extend the statute of limitations, and it gives an example of a Form 1040X disclosing extra income that the IRS could not assess because the original three-year period had already closed and neither 6501(e) prong applied. The narrow exception is section 6501(c)(7): if the IRS receives a signed amended return showing additional tax within the 60 days before the assessment period would otherwise expire, the period for assessing that additional amount does not expire until 60 days after receipt.

This cuts both ways. Once the statute on a year has closed, the IRS generally cannot assess tax for it even if you volunteer the missing figures. But whether a year is actually closed depends on the analysis above: an omission over 25 percent, or over $5,000 from a foreign asset, keeps it open for six years; an unfiled Form 5471, 8938 or 8621 can keep it open indefinitely. Most UK-resident Americans who assume that their old years are closed have not tested either condition.

How should missed US tax returns and omitted UK income be put right?

The statute of limitations analysis does not choose the remedy by itself, but it defines the exposure the remedy has to address. We map every year before anything is filed, and in practice the options fall into three groups.

Amended returns only. Where the omission is modest, all information returns were filed, and FBARs were filed on time, a straightforward Form 1040X for the affected open years may be proportionate. The Toso and disclosure points can matter here in deciding which years are truly open.
Streamlined Foreign Offshore Procedures. For non-wilful filers who meet the non-residency test, the IRS page at https://www.irs.gov/individuals/international-taxpayers/us-taxpayers-residing-outside-the-united-states requires delinquent or amended returns for each of the most recent three years for which the due date has passed, delinquent FBARs for each of the most recent six years, and a Form 14653 certification of non-wilful conduct. Eligible filers are not subject to failure-to-file, failure-to-pay, accuracy-related, information return or FBAR penalties; tax and interest are still due.
Full catch-up for missed US tax returns. Where returns were never filed at all, section 6501(c)(3) means no year is closed by the passage of time. The streamlined route still generally defines the look-back for non-wilful filers, and outside it the IRS applies a long-standing internal policy of normally pursuing delinquent returns for no more than six years. That six-year filing policy is administrative practice, not statute, and we cover it separately on this site.

The three-year streamlined window and the six-year 6501(e) period are not the same thing and should not be confused. The procedures specify what you file to obtain the penalty terms; they do not rewrite section 6501. The general streamlined page at https://www.irs.gov/individuals/international-taxpayers/streamlined-filing-compliance-procedures explains the programme's scope and processing. Our own team handles the full streamlined filing at https://www.us-uktax.com/streamlined-foreign-offshore-procedures, and you can estimate the years and forms involved using https://www.us-uktax.com/calculators/streamlined-filing-calculator before speaking to us.

How does the FBAR six-year penalty statute differ from section 6501(e)?

The FBAR is not a tax return and is not governed by the Internal Revenue Code's assessment rules at all. It sits in Title 31. Under 31 USC 5321(b)(1), at https://www.law.cornell.edu/uscode/text/31/5321, the Treasury may assess a civil FBAR penalty at any time before the end of the six-year period beginning on the date of the transaction with respect to which the penalty is assessed; for a missed FBAR, that period is generally measured from the date the report was due. Section 5321(b)(2) then allows two years from assessment to bring a civil action to recover it.

The coincidence of six years in both regimes causes confusion. The FBAR period runs independently for each year and does not depend on any income omission, whereas section 6501(e) depends on the size and source of omitted income on a filed tax return. A person can have a closed income tax year and an open FBAR year, or the reverse. Late FBARs are filed electronically through FinCEN's BSA E-Filing System at https://bsaefiling.fincen.treas.gov with an explanation for late filing, and the IRS overview of the FBAR requirement is at https://www.irs.gov/businesses/small-businesses-self-employed/report-of-foreign-bank-and-financial-accounts-fbar for reference.

What does this mean on the UK side?

Most of the income that triggers section 6501(e) for UK residents is income HMRC never taxes: ISA interest, dividends and gains are exempt in the UK, as GOV.UK explains at https://www.gov.uk/individual-savings-accounts, the official ISA guidance. That is exactly why it is left off US returns: the UK tax return does not show it, UK platforms do not issue US-style tax statements, and a preparer working from the Self Assessment return alone will never see it. The US, by contrast, does not recognise the ISA wrapper at all.

Where the omitted item is UK-taxable, such as rental profit or a bonus, the UK side usually already has it, and the US correction is primarily about the foreign tax credit rather than new money. HMRC operates its own, separate time limits for assessment, which lengthen where an inaccuracy was careless or deliberate, and the two regimes do not align. When we prepare catch-up filings we reconcile each US year to the corresponding UK tax year, which runs from 6 April to 5 April, so that nothing reported in one country contradicts the other. Our US return service is at https://www.us-uktax.com/us-tax-services and our UK return service at https://www.us-uktax.com/uk-tax-services for the HMRC side.

A practical checklist before you decide which years are open

List every year in which a return was filed, and separately every year in which none was filed; the second group is governed by 6501(c)(3), not 6501(e).
For each filed year, total the gross income actually stated, using gross receipts for any trade or business.
Quantify the omitted gross income, excluding amounts adequately disclosed, adding back any overstated basis, and counting only the current-year portion of PFIC gains.
Test the 25 percent prong, then separately test whether more than $5,000 of the omission came from a specified foreign financial asset.
Check every information return obligation, including Forms 5471, 926, 8938 and 8621, because a missing one engages 6501(c)(8).
Map the FBAR years separately under 31 USC 5321(b)(1), then choose between amendments, the streamlined route or a full catch-up.

If you want the analysis done for you, year by year, with the US and UK returns reconciled, contact us at https://www.us-uktax.com/contact today. We prepare the returns, the information forms and the FBARs as one filing, so that the statute position you rely on is the one the paperwork actually supports.