Is a UK money market fund a PFIC for a US citizen?

Yes, in practice. A money market fund earns almost entirely interest and holds almost entirely passive assets, so it meets both the 75 percent income test and the 50 percent asset test in section 1297. That applies whether the fund is sterling or dollar denominated, and whether it is held directly, through a UK platform, or inside an ISA. A Form 8621 is generally required for each fund or share class held.

Does the UK tax money market fund distributions as dividends?

Usually not. Under section 378A of ITTOIA 2005, a distribution from an offshore fund is treated as interest if more than 60 percent of the fund's assets by market value are qualifying, interest-bearing investments, which describes any money market fund. The income is reported as savings income on the UK return, so the dividend allowance and dividend rates do not apply. UK-authorised funds follow a parallel domestic rule.

Can I avoid PFIC rules by holding a US money market fund from the UK?

Yes, a US-domiciled money market fund is not a PFIC, so there is no Form 8621 and, if held at a US brokerage, no FBAR or Form 8938 for that holding. The trade-off is on the UK side: the fund is an offshore fund, distributions are taxed as interest, and any disposal gain from a non-reporting fund is an offshore income gain charged to income tax rather than capital gains tax.

Can I make a mark-to-market election on an Irish money market fund?

Often. Treasury Regulations section 1.1296-2(d) treats shares redeemable at net asset value as marketable if the fund meets conditions including more than 100 shareholders in the class, public availability with no minimum initial investment above $10,000, weekly published prices, audited accounts, government regulation and at least 90 percent passive income and assets. Institutional share classes with high minimums frequently fail, so the specific class must be checked.

Do I report a UK money market fund on FBAR and Form 8938?

Yes. The IRS treats foreign mutual funds as reportable on both forms. If the fund sits inside a UK platform, private bank or ISA account, the account is reported and its contents need not be listed separately. FBAR applies when aggregate foreign accounts exceed $10,000 at any time in the year; for US citizens living abroad, Form 8938 applies above $200,000 at year end or $300,000 at any time for single filers.

Why did my cash fund trigger an excess distribution when I sold nothing?

Because an excess distribution is measured against prior distributions, not gains. Any current-year distribution above 125 percent of the average of the previous three years is an excess distribution under section 1291. When short-term interest rates rise, a money market fund's payouts can jump past that line even though its share price never moves. The excess is spread over the holding period and attracts an interest charge unless an election is in place.

US UK Tax Returns Preparation for Money Market Fund Cash

US UK tax returns preparation for money market fund cash comes down to one question: where is the fund domiciled? For a US citizen living in the UK, a sterling or dollar money market fund domiciled in the UK, Ireland or Luxembourg is almost always a passive foreign investment company (PFIC) for US purposes, reportable on Form 8621 and taxed under the punitive excess distribution regime unless an election is made. A US-domiciled money market fund avoids the PFIC rules entirely, but the UK then treats it as an offshore fund, and its distributions are normally taxed in the UK as interest rather than dividends.

Neither choice is automatically wrong. What goes wrong is holding a large cash balance in a fund without knowing which rules apply on each side of the Atlantic. In the returns we prepare for high-net-worth clients, money market funds are among the most common sources of an unexpected Form 8621, and of UK income coded as dividends when it should have been reported as interest. This guide covers how we handle both returns, the elections that matter, the reporting forms, and a worked comparison of the same cash held four ways.

What is a money market fund for US and UK tax purposes?

A money market fund is a pooled investment vehicle that holds very short-dated, high-quality debt and deposits, such as government bills, commercial paper and bank deposits, aiming to preserve capital while paying a return close to short-term interest rates. Wealth managers often sweep surplus cash into one automatically.

Tax law does not care that the fund behaves like cash. For US purposes, a non-US money market fund is a foreign corporation earning passive income, which places it within the PFIC definition. For UK purposes, a non-UK fund is generally an offshore fund, and a fund invested mostly in interest-bearing assets pays distributions the UK taxes as interest.

Is a UK or Irish money market fund a PFIC for a US citizen?

Yes, in practically every case we see. Under 26 U.S.C. section 1297, set out at https://www.law.cornell.edu/uscode/text/26/1297, a foreign corporation is a PFIC if 75 percent or more of its gross income for the year is passive income, or if at least 50 percent of its assets, on average, produce passive income or are held to produce it. A money market fund's income is essentially all interest and similar returns on short-term instruments, and its assets are essentially all passive. It meets both tests comfortably.

The statute does contain an exception for income derived in the active conduct of a banking business, but it applies to institutions licensed to do business as a bank in the United States, not to an investment fund. We have not found any special US rule that removes foreign money market funds from the PFIC regime, so we prepare returns on the basis that a UK, Irish or Luxembourg money market fund held by a US citizen is a PFIC, whether it is denominated in sterling, dollars or euros, and whether it is held directly or through a UK platform or private bank account.

A UK ISA wrapper does not change this either. The IRS does not recognise the ISA as tax-favoured, so a money market fund held inside a stocks and shares ISA is still a PFIC held by a US person, and the ISA account itself is a foreign financial account for US reporting.

How does Form 8621 work for a non-US money market fund?

Form 8621 is the annual information return a US person files for each PFIC. The IRS instructions at https://www.irs.gov/instructions/i8621 require a separate Form 8621 for each PFIC held directly or indirectly, and a filing is generally triggered when the shareholder receives certain distributions, recognises gain on a disposition, reports under a QEF or mark-to-market election, makes an election, or is required to file an annual report under section 1298(f). Each share class or fund is a separate PFIC, so a client with three cash funds across two platforms can easily need three or more forms a year.

There is a limited exception from completing Part I. According to the instructions, a shareholder does not need to complete Part I for a section 1291 fund if the aggregate value of all PFIC stock owned at the end of the tax year falls within the threshold and the shareholder neither received an excess distribution from, nor recognised gain on a disposition of, that fund. Joint filers have a combined threshold of $50,000. For the high-net-worth readers we serve, parking seven-figure cash balances in these funds, the exception is rarely available, and it never removes the need to report an excess distribution or a gain.

There are three ways a PFIC can be taxed, and the choice has to be made deliberately, ideally in the first year the fund is held.

Section 1291 (the default excess distribution regime): ordinary distributions are taxed as ordinary income, but any distribution above 125 percent of the average of the prior three years, and any gain on disposal, is treated as an excess distribution, allocated across the holding period and subject to tax at the highest rate for each prior year plus an interest charge.
Qualified electing fund (QEF) election: the shareholder includes a pro rata share of the fund's ordinary earnings and net capital gain each year. It requires the fund to supply a PFIC Annual Information Statement, which many non-US money market funds do not produce.
Mark-to-market election under section 1296: the shareholder includes the annual increase in value as ordinary income, and deducts decreases to the extent of prior inclusions. It is available only for marketable stock, which for a money market fund turns on the regulatory test discussed below.

Why do rising interest rates create an excess distribution trap?

This is the first gap we rarely see covered elsewhere. PFIC commentary tends to assume the excess distribution regime only bites when a fund is sold at a gain. A distributing money market fund holds its value steady, so clients assume there is never an excess distribution. That assumption fails when interest rates rise.

The IRS instructions define an excess distribution as the portion of a current-year distribution that exceeds 125 percent of the average distributions received on that stock over the prior three years, or the shorter holding period. No distribution received in the first year of the holding period is an excess distribution. A money market fund's distributions track short-term rates almost exactly. If rates move from near zero to a meaningful level over two or three years, this year's distribution can easily exceed 125 percent of the three-year average, even though the client has not sold anything and the share price has not moved.

The excess portion is then allocated day by day across the holding period. The part allocated to the current year and to any pre-PFIC years is ordinary income; the part allocated to earlier PFIC years is taxed separately at the highest applicable rate for each of those years, with an interest charge under section 1291(c). The amounts are often modest relative to the balance, but the computation, the interest charge and the Form 8621 reporting are all required, and we regularly see returns from prior preparers that report these distributions simply as foreign dividends with no Form 8621 at all.

The reverse problem affects accumulating share classes. An accumulating fund pays no distributions; the return builds up in the share price. Under the default regime, there is nothing to report until disposal, when the whole gain is treated as an excess distribution spread back across every year of holding. For a large balance held for several years, that produces a sizeable deferred tax and interest charge in the year the client finally withdraws the cash to buy a property or fund a business.

Can a US citizen make a mark-to-market election on a money market fund?

Often yes, and this is the second gap angle. Most commentary treats the mark-to-market election as available only for listed shares, such as exchange-traded funds. That is incomplete. The IRS instructions confirm that marketable stock includes stock in certain PFICs described in Treasury Regulations section 1.1296-2(d), and that regulation, at https://www.law.cornell.edu/cfr/text/26/1.1296-2, extends marketable status to a foreign fund whose shares are redeemable at net asset value if it meets a set of conditions for the share class the electing taxpayer holds.

More than 100 shareholders in the class throughout the year, ignoring related persons.
Shares available for purchase by the public at net asset value throughout the year, with no minimum initial investment above $10,000.
Prices quoted at least weekly in a widely available medium the fund does not control.
Annual financial statements prepared by independent auditors and made public.
Regulation as an investment company by a foreign government or agency with broad enforcement powers.
No senior securities and no more than de minimis debt.
At least 90 percent of gross income passive, and on average at least 90 percent of assets held for passive income.

A mainstream regulated UK, Irish or Luxembourg money market fund will often satisfy most of these conditions. The condition that most often fails in practice is the minimum investment. Private banks frequently place high-net-worth clients in institutional or premier share classes with minimum subscriptions well above $10,000, and the test applies to the specific class held. When we prepare a first-year return, we check the share class documents before recommending that the client make the election, because an election made on a class that does not qualify is ineffective and leaves the client in the default regime.

Where the election is available, the annual return of a stable-value fund is taxed as ordinary income each year, broadly as bank interest would be, without the interest charge. For a fund already held for several years without an election, the transition year has its own rules.

How does the UK tax a US money market fund held by a UK resident?

A US citizen who sidesteps the PFIC rules by holding a US-domiciled money market fund through a US brokerage account solves the US problem but creates a UK one. The UK offshore fund rules apply to non-UK funds, and a US mutual fund generally falls within the offshore fund definition. HMRC's manual at https://www.gov.uk/hmrc-internal-manuals/investment-funds/ifm12410 explains that a reporting fund is an offshore fund that has applied for and been approved as a reporting fund, and that HMRC publishes the list of approved reporting funds on GOV.UK, updated monthly.

Reporting status determines how a gain on disposal is taxed. For a reporting fund, a gain is normally a capital gain. For a non-reporting fund, the gain is an offshore income gain charged to income tax rather than capital gains tax. US money market funds are typically not on the reporting fund list, because they are not marketed to UK investors and have no reason to apply. In practice this matters less for a stable-value money market fund than for an equity fund, because there is little or no gain on disposal. The bigger UK question is how the distributions are characterised.

Does the UK tax money market fund distributions as interest or dividends?

As interest, in almost every case. Section 378A of the Income Tax (Trading and Other Income) Act 2005, at https://www.legislation.gov.uk/ukpga/2005/5/section/378A, provides that a dividend paid by an offshore fund is treated as interest for income tax purposes if the fund fails the qualifying investments test at any time in the relevant period. The fund fails if the market value of its qualifying investments exceeds 60 percent of the market value of all its assets, excluding cash awaiting investment. Qualifying investments broadly means interest-bearing and economically similar assets, which is exactly what a money market fund holds.

This is the bond fund rule in its offshore form. It means distributions from a US, Irish or Luxembourg money market fund are reported on the UK return as savings income, not dividend income. The dividend allowance does not apply, and the higher dividend rates do not apply either; instead the income is taxed at the savings rates, with whatever personal savings allowance the client's income level permits. UK-authorised money market funds follow a parallel domestic regime under which funds invested mostly in interest-bearing assets pay interest distributions. In the returns we review, the most frequent UK error is entering a US fund's Form 1099-DIV figure as a foreign dividend simply because the US form calls it a dividend.

How are US money market fund dividends taxed on the US return?

A US money market fund is a domestic regulated investment company, not a PFIC, so its distributions are reported on Form 1099-DIV and taxed as ordinary dividends on the Form 1040. Because the underlying income is interest, these distributions are generally not eligible for the reduced qualified dividend rates. Some US funds designate a portion of their distributions as interest-related dividends; that designation exists to relieve non-resident aliens from US withholding and does not change the position for a US citizen, who is taxed on the full distribution regardless.

A domestic money market fund held through a US brokerage account is not a foreign financial asset, so it does not appear on FBAR or Form 8938, and there is no Form 8621.

How does the foreign tax credit work on money market fund income?

Both countries tax the same income, so double tax relief is central to the preparation. For a UK-domiciled or Irish fund, the income is foreign source for US purposes and UK tax paid on it is creditable on Form 1116 in the passive category, subject to the usual limitation. Because the UK taxes the distributions as interest at savings rates and the US taxes them as ordinary income, the UK tax often covers most or all of the US liability on the ordinary portion, although any PFIC interest charge is not a tax that the foreign tax credit can offset in the same way.

For a US money market fund or US Treasury bills, the income is US source. The UK, as country of residence, taxes it and the US-UK income tax treaty's relief article and saving clause govern the interaction. In broad terms, the UK gives credit only for the US tax that the treaty would allow the US to charge a non-citizen on that income, and the US then re-sources enough of the income to allow a US credit for the UK tax that remains. The mechanics need to be worked through line by line on both returns, and we prepare them together for exactly this reason: preparing the US and UK returns separately is the most common way clients end up paying more than the higher of the two taxes.

What FBAR and Form 8938 reporting applies to money market funds?

The IRS comparison at https://www.irs.gov/businesses/comparison-of-form-8938-and-fbar-requirements sets out the position. An FBAR (FinCEN Form 114) is required where the aggregate value of foreign financial accounts exceeds $10,000 at any time during the calendar year, filed electronically through FinCEN's BSA E-Filing System by April 15 with an automatic extension to October 15. Form 8938 is attached to the income tax return; for taxpayers living abroad the threshold is more than $200,000 at year end or more than $300,000 at any time for single filers, and more than $400,000 at year end or more than $600,000 at any time for joint filers.

A UK or Irish money market fund held directly is a foreign mutual fund, reportable on both FBAR and Form 8938.
A UK platform, private bank or ISA account holding the fund is a foreign financial account; the account is reported, and its contents need not be listed separately on either form.
A UK deposit account is reportable on FBAR and, above the thresholds, on Form 8938.
A US money market fund or Treasury bills held at a US brokerage are not foreign assets and appear on neither form.
A domestic fund investing in foreign securities is not reportable on either form.

Where reporting was missed in earlier years, late FBARs are filed through the BSA E-Filing System with a reason for late filing, or as part of the Streamlined Filing Compliance Procedures. For a UK-resident US citizen who qualifies, the Streamlined Foreign Offshore Procedures carry no penalty, and they are the route we most often use to bring missing Forms 8621 and FBARs up to date.

How does the same cash compare across four places to park it?

The following worked scenario is an illustration only. Assume a US citizen resident in the UK, taxed on the arising basis, holds £2,000,000 of surplus cash for a full year earning an assumed 4 percent, or £80,000. We assume an exchange rate of $1.30 to £1 purely for illustration, so the balance is roughly $2.6 million, and we deliberately do not compute final tax figures, because the outcome depends on the client's other income, rate bands and treaty position.

Option one, a UK-domiciled or Irish sterling money market fund, distributing class, no election. UK side: the £80,000 is savings income, taxed as interest. US side: the fund is a PFIC. Suppose prior distributions were £20,000, £40,000 and £60,000 as rates rose, an average of £40,000. 125 percent of that average is £50,000, so £30,000 of this year's distribution is an excess distribution, allocated across the holding period, with part taxed at the highest prior-year rates plus an interest charge. Reporting: Form 8621, Form 1116, FBAR and Form 8938.

Option two, the same fund with a valid mark-to-market election. UK side unchanged. US side: the £80,000 annual return, converted to dollars, is ordinary income each year with no interest charge, and the UK tax is creditable against it. Reporting: still Form 8621, FBAR and Form 8938, but the computation is simple. The election only works if the share class meets the regulatory conditions, including the $10,000 maximum minimum investment.

Option three, a US dollar money market fund at a US brokerage. US side: ordinary dividends on Form 1099-DIV, no PFIC. UK side: an offshore fund whose distributions are treated as interest under section 378A, with any disposal gain an offshore income gain if the fund is non-reporting. Treaty relief applies to US-source income. Reporting: no Form 8621, FBAR or Form 8938 for this holding. Currency exposure now sits on the UK side, because the UK measures the income in sterling.

Option four, a UK bank deposit or US Treasury bills. A UK deposit produces plain interest on both returns, with UK tax creditable in the US, and FBAR and Form 8938 reporting for the account. Treasury bills held at a US broker produce US-source interest on the US return, no PFIC and no foreign account reporting; on the UK side the return arrives as a discount on redemption rather than a coupon, which the UK generally taxes as income, so the timing of recognition on the two returns needs to be aligned. In our experience, options two, three and four produce similar overall tax for a client already paying UK higher rates; option one without an election is the outlier.

What currency issues arise with dollar and sterling cash funds?

The US return is prepared in dollars and the UK return in sterling, so one side always measures a currency movement. A sterling fund held by a US citizen produces a dollar result that includes the movement of sterling, which flows into the PFIC computation or mark-to-market inclusion. A dollar fund held by a UK resident produces sterling-measured income and, on disposal, a sterling-measured gain or loss. We record transaction-date exchange rates for every subscription, distribution and redemption, because reconstructing them years later is far harder.

What does US UK tax returns preparation involve for money market fund holders?

We start with a map of every place the client's cash sits, identifying which holdings are PFICs, which are UK offshore funds and which are neither, and we collect each fund's domicile, share class, minimum investment, distributing or accumulating status, distributions and UK reporting status. We then test PFIC share classes against the mark-to-market conditions, compute any excess distributions, prepare Forms 8621, 1116, 8938 and the FBAR, and prepare the UK self assessment with fund distributions reported as interest. Missed years go through the Streamlined procedures. The result is two returns that agree with each other.