Introduction: Short Selling Is Taxed Twice, in Two Different Years
Short selling creates a tax problem for an American in London that almost no broker, bank or published guide explains: the IRS and HMRC tax the same short position, but they tax it in different years and under different rules. The United States waits until you close the position. Britain, by contrast, treats the original sale as the disposal and places the gain in the tax year you opened the trade.
For a sophisticated investor running hedged positions, that mismatch matters a great deal. Furthermore, the dividend you pay to the stock lender is deductible in one country and worthless in the other. Additionally, the foreign tax credit that normally prevents double taxation can land in the wrong year entirely. At TaxYork, we prepare returns for investment bankers, fund principals and company owners who use short selling as part of a wider portfolio, and the same errors appear every season.
Why Short Selling Breaks the Usual Cross-Border Rules
Most cross-border investment income follows a simple pattern. You buy an asset, you sell it, and both countries recognise the gain in roughly the same period. Short selling reverses the order of events, because you sell shares you have borrowed before you own anything at all. Consequently, each tax system must decide when the disposal happens, and the two systems answer that question differently.
This guide covers the US rules under section 1233, the treatment of substitute dividends, the HMRC share identification rules, the foreign tax credit timing problem, and the reporting obligations that follow a UK or US brokerage account. Above all, it explains how to keep one trade from producing two unrelieved tax bills.
Who This Guide Is For
We wrote this for US citizens and green card holders who are resident in the United Kingdom and who use short selling on listed shares through a US or British broker. It also suits dual nationals and accidental Americans who discover that their trading history has never reached an American return. Spread bets and contracts for difference work differently, and we explain where they diverge below.
How the IRS Taxes Short Selling
The IRS treats short selling as an open transaction until you deliver shares to the lender. Specifically, IRS Publication 550 on investment income and expenses confirms that a short sale is not complete until you close it, so the gain or loss belongs to the tax year of closing. You report it on Form 8949 for that year, with the original sale proceeds as the proceeds and the cost of the covering shares as the basis.
The Holding Period Under Section 1233
Whether the result is short-term or long-term depends on how long you held the shares you deliver to close the position. In practice, most investors who engage in short selling buy to cover and deliver almost immediately, so the gain is almost always short-term. Therefore, a profitable short is usually taxed at ordinary rates of up to 37%, plus the 3.8% net investment income tax once your income passes $200,000 single or $250,000 joint.
Moreover, section 1233 of the Internal Revenue Code adds two anti-abuse rules. Under section 1233(b), if you held substantially identical shares for one year or less when you opened the short, any gain on closing is short-term. In addition, the holding period of those long shares restarts. Under section 1233(d), if you held substantially identical shares for more than one year, any loss on closing is long-term. Together, these rules stop investors from using short selling to convert short-term gains into long-term gains through paired positions.
Why the 2026 Rate Thresholds Rarely Help
The 2026 inflation adjustments in Revenue Procedure 2025-32 set the 20% long-term rate threshold at $545,500 for single filers and $613,700 for joint filers. However, those preferential rates only matter if your covering shares were held for more than a year. For typical tactical short selling, the gain is ordinary income in all but name. As a result, a wealthy investor in London can face a combined US rate of 40.8% on short selling profits before any credit for British tax.
Losses, Wash Sales and Straddles
Losses on short selling are capital losses, so they offset capital gains without limit but only $3,000 of ordinary income each year. Furthermore, section 1091 extends the wash sale rules to short positions under subsection (e), so closing a short at a loss and reopening it within 30 days can defer the loss. Similarly, the straddle rules can defer a loss on one leg of a hedge until you close the offsetting leg. We explain the interaction with British share matching in our guide to wash sale rules and UK bed and breakfasting.
Substitute Dividends: The Cost Nobody Prices In
When you hold a short position over a dividend record date, you must pay the lender an amount equal to the dividend. This is a substitute payment, sometimes called a payment in lieu of a dividend, and it is a real cash cost of short selling. However, the two tax systems treat it in completely different ways.
The 45-Day Rule in Section 263(h)
Under section 263(h), if you close the short within 45 days of opening it, you cannot deduct the substitute payment. Instead, you add it to the basis of the shares you deliver, which reduces your gain or increases your loss. If the short stays open for more than 45 days, the payment becomes deductible as investment interest. For an extraordinary dividend, the waiting period extends to one year.
Notably, several published guides misstate the extraordinary dividend test. Section 263(h) borrows the definition in section 1059(c), under which a dividend is extraordinary when it equals or exceeds 10% of the measuring amount for ordinary shares, or 5% for preferred shares. However, for a short seller the measuring amount is the amount you realised on the short sale, not a basis you never had. Special dividends from British companies returning surplus capital can cross that line, so check every large payment before you assume a deduction.
Furthermore, section 263(h)(4) suspends the 45-day clock for any period in which you hold, or have an option to buy, substantially identical shares. In other words, a hedged short does not start counting until the hedge comes off. Many investors who believe they have passed the 45-day mark have not.
Investment Interest and the Standard Deduction Trap
A deductible substitute payment is investment interest under section 163(d), claimed on Form 4952 and limited to your net investment income. Crucially, it is an itemised deduction. For 2026, the standard deduction is $16,100 for single filers and $32,200 for joint filers. Consequently, many Americans in London who claim the foreign tax credit, and who therefore have few other itemised deductions, receive no benefit at all from substitute payments below those amounts.
Stock borrow fees raise a separate problem. In our view, borrow fees on hard-to-borrow shares are better characterised as investment expenses than as interest. Since the One Big Beautiful Bill Act made the suspension of miscellaneous itemised deductions permanent, those fees generally produce no US deduction.
The British Treatment of Manufactured Dividends
HMRC calls the same payment a manufactured dividend. Its guidance on manufactured payments in the Corporate Finance Manual explains the regime, and the rule for an individual who is not a financial trader is blunt: the payment is not allowable as a deduction against income. Therefore, a British resident who shorts a high-yield stock pays the dividend out of taxed money on both sides of the Atlantic. Our analysis of securities lending and manufactured payments covers the mirror position for the lender.
How HMRC Taxes Short Selling
Britain charges capital gains tax on short selling of shares in the same way as any other share disposal, at 18% for basic rate taxpayers and 24% for higher and additional rate taxpayers, as the official capital gains tax rates confirm. The annual exempt amount remains £3,000. However, the timing rule is where Britain parts company with America.
The Disposal Happens When You Sell
Under British law, short selling is a disposal on the date you sell the borrowed shares. HMRC then needs to identify which acquisition matches that disposal. The share identification rules in section 106A of the Taxation of Chargeable Gains Act 1992 and HMRC manual CG51555 on identifying disposals apply a fixed order. First, shares bought on the same day. Second, shares bought within the following 30 days. Third, the section 104 pool. Finally, acquisitions after the disposal, earliest first.
That final rule is the one that governs conventional short selling. If you hold no shares in the company, HMRC matches your sale with the later purchase you make to cover it, even if that purchase comes months later. Nevertheless, the gain still belongs to the tax year of the original sale. As a result, a short opened in March and closed in September produces a British gain in the earlier tax year and a US gain in the later calendar year.
Short Against the Box Under British Rules
The matching order creates a serious trap for investors who short a stock they already own. If you hold shares in a section 104 pool and open a short for more than 30 days, HMRC matches the short sale against your pool. In effect, Britain treats you as having sold your long holding, crystallising the gain immediately.
The United States reaches a similar result by a different route, because the constructive sale rules in section 1259 treat a short against the box on an appreciated position as a sale. However, the basis, the timing and the currency translation rarely line up precisely. We explore that hedge in depth in our guide to the constructive sale rules for Americans in Britain.
Filing When the Position Is Still Open
The British approach to short selling creates a practical difficulty. If you open a short in February and the position remains open on 31 January of the following year, you must file a return for a disposal whose cost you do not yet know. In that case, you file on time using a provisional figure, explain it in the additional information box, and amend once you close. Ignoring the disposal is not an option, because HMRC treats a missing gain as an inaccuracy, not a timing preference.
Furthermore, you must report any year in which your total disposal proceeds exceed £50,000, even if the net gain is small. Active short selling easily crosses that proceeds test. HMRC's guidance on tax when you sell shares sets out the reporting thresholds, and its page on capital losses explains the four-year claim window for losses.
Stamp Duty Reserve Tax and Trading Status
When you buy British shares to close a short, the covering purchase normally attracts stamp duty reserve tax at 0.5%. The original short sale does not, because you are the seller. The Stamp Taxes on Shares Manual covers the reliefs available to intermediaries, but private investors rarely qualify. Additionally, a very high volume of short selling can prompt HMRC to argue that you are trading, which would move profits into income tax at up to 45%. For most private investors, however, capital treatment applies.
Spread Bets, CFDs and Disclosure Rules
Many British investors never short real shares at all. Instead, they use financial spread bets or contracts for difference, which each have their own tax treatment. For an American, however, the choice of instrument for short selling changes the outcome dramatically.
Spread Betting Is Tax-Free Only in Britain
HMRC treats a personal spread bet as gambling, so profits sit outside capital gains tax. However, the IRS recognises no such exemption. A US citizen must report spread betting gains on the American return with no British tax to credit, which often makes a spread bet the most expensive way to go short. Our guide to spread betting and US tax works through the arithmetic.
CFDs Follow a Third Set of Rules
Contracts for difference are taxed by HMRC as financial futures under its capital gains guidance on contracts for differences, with financing costs and dividend adjustments folded into the gain. The US characterisation is far less settled, and the swap regulations can produce ordinary income. Therefore, a short via a CFD is not a substitute for physical short selling from a US tax perspective. See our detailed guide to CFD trading tax for Americans in Britain.
FCA Net Short Position Reporting From July 2026
Regulatory disclosure for short selling sits alongside the tax position. Under the reformed UK regime, you must notify the Financial Conduct Authority when a net short position reaches 0.2% of a company's issued share capital, and at each 0.1% increment above that. From 13 July 2026, the FCA publishes only an aggregated, anonymised figure for each company rather than naming individual holders. The FCA's notification and disclosure page sets out the deadlines.
The Foreign Tax Credit Timing Problem
The central risk in cross-border short selling is not the rate of tax. Instead, it is that the British tax and the American tax fall into different years, so the foreign tax credit may not offset the US liability on the same gain.
Is the Gain Foreign-Source?
Under section 865, gains from selling personal property are generally sourced by residence. A US citizen living in Britain is treated as a non-resident for this purpose only if their tax home is abroad and they pay at least 10% foreign tax on the gain. At 24% British capital gains tax, that test is normally met. Consequently, the gain is foreign-source passive income, and British tax can be credited against it. However, if you use brought-forward British losses to reduce the UK tax below 10%, the gain reverts to US-source and the credit disappears.
Accrual Versus Cash Method for Credits
By default, an individual claims foreign tax credits in the year the tax is paid, which suits short selling poorly. British capital gains tax for the 2025/26 year is paid on 31 January 2027, while the US may tax the same short in 2026. Therefore, a cash-method taxpayer can end up with US tax in 2026 and the matching credit in 2027. Excess credits carry back one year and forward ten, but only within the passive category basket.
Alternatively, section 905 allows you to elect the accrual method, under which British tax accrues at the end of the UK tax year on 5 April. In our experience, that election aligns British and American years more closely for active investors. However, it is irrevocable, so model it before you make it. Our guide to foreign tax credit basket errors covers the basket rules in more depth.
Currency Translation on Each Leg
The IRS requires dollar figures for each leg of a sterling trade. You translate the short sale proceeds at the spot rate on the sale date and the covering purchase at the spot rate on the purchase date. As a result, short selling that makes a modest sterling profit can produce a larger or smaller dollar gain, and the British tax translated into dollars will rarely match the US tax on the same gain.
FBAR, Form 8938 and Missed Reporting
Short selling usually happens inside a margin account, and the account itself triggers reporting regardless of whether the trades made money. Furthermore, missed reporting on a brokerage account is one of the most common gaps we find when new clients arrive.
Reporting a British Brokerage Account
A margin account with a British broker is a foreign financial account. If the aggregate maximum value of your foreign accounts exceeds $10,000 at any point in the year, you must file an FBAR through the FinCEN BSA E-Filing System, as the IRS guidance on the FBAR explains. Report the maximum account value as the broker values it, and never net a liability in one account against assets in another.
In addition, Form 8938 applies to Americans abroad with specified foreign financial assets above $200,000 at year end or $300,000 at any time for single filers, and double those figures for joint filers. The IRS comparison of Form 8938 and FBAR requirements shows how the two overlap. Our FBAR and FATCA reporting service handles both filings together.
When a US Broker Account Hides the Problem
A US brokerage account does not need an FBAR. However, it creates the opposite gap, because the United States does not exchange data under the Common Reporting Standard. HMRC therefore relies on you to report gains from US accounts. In our experience, Americans who short through a US broker frequently file accurate US returns while omitting the same gains from Self Assessment. If that applies to you, read our guide to missed UK tax returns for Americans before HMRC contacts you.
Catching Up on Missed Years
Where US returns or FBARs were missed, the IRS Streamlined Foreign Offshore Procedures remain the standard route for non-wilful taxpayers living abroad. Our IRS Streamlined filing service prepares the three years of returns and six years of FBARs together, with the short selling history reconstructed from broker statements. On the British side, an unprompted disclosure attracts lower penalties than one made after HMRC opens an enquiry.
Case Study: A Short Opened in One Tax Year and Closed in Another
The following illustrative case study shows how a single profitable piece of short selling creates two tax bills in different years. The figures are rounded, and the client details are anonymised.
The Facts
James is a US citizen who has lived in London since 2015 and pays additional rate tax. On 10 March 2026, he borrows and sells 20,000 shares in a FTSE 250 company at £25, raising £500,000. In May 2026, the company pays a 60p dividend, so James pays a £12,000 manufactured dividend to the lender. On 15 September 2026, he buys 20,000 shares at £18 for £360,000, plus £1,800 of stamp duty reserve tax, and closes the position.
The British Position
Because James sold on 10 March 2026, the disposal falls in the 2025/26 tax year. He holds no other shares in the company, so HMRC matches the sale with the September purchase. His gain is £500,000 less £361,800, or £138,200. The manufactured dividend is not deductible. After the £3,000 annual exempt amount, he pays 24% on £135,200, which is £32,448, due on 31 January 2027.
The US Position
For the IRS, the short closed in September 2026, so the gain belongs on the 2026 return. Translating proceeds at $1.35 gives $675,000, and translating the covering cost at $1.33 gives a basis of $481,194, including stamp duty. His short-term gain is therefore $193,806. Because the position stayed open for more than 45 days, the $16,080 substitute payment is investment interest. However, James has no other itemised deductions, so it falls below the $16,100 standard deduction and saves nothing.
At 37%, the US tax on the gain is $71,708, plus $7,365 of net investment income tax. James had made the accrual election several years earlier, so his 2025/26 British tax accrues on 5 April 2026 and falls into his 2026 credit computation. The £32,448 of British tax, roughly $43,500, offsets most of the regular US tax, leaving about $28,200 of residual US tax plus the net investment income tax.
The Lesson
Had James been on the cash method, the British tax would have been paid in January 2027, leaving his 2026 US liability uncovered and creating a carryback claim. Furthermore, the manufactured dividend cost him £12,000 with no relief in either country. In our view, short selling a high-yield British stock over a record date is rarely worth it for an American investor once both tax systems are priced in.
How TaxYork Can Help
We prepare the full cross-border position for active investors, from Form 8949 and Form 4952 to the Self Assessment capital gains pages and the foreign tax credit computation. Moreover, we reconcile broker statements in both currencies, so every leg of a short is translated correctly and matched under both countries' rules. Our US tax returns for expats service covers the annual filing, while our tax treaty optimisation service models the credit timing before you trade.
Where earlier years contain unreported short selling gains, we manage the catch-up on both sides, including FBARs, amended Self Assessment returns and disclosure to HMRC. Additionally, investors who trade at scale should review our guide to the section 475(f) trader election, which changes the treatment of short positions entirely.
Conclusion
Short selling is one of the few investment strategies where the US and British tax systems disagree about the year of the gain itself. The IRS waits until you close, while HMRC taxes the sale when you make it. Furthermore, substitute dividends receive relief only in narrow circumstances in America and none at all in Britain. As a result, an American in London who shorts shares without planning can pay tax twice in different years and recover only part of it.
The solution is to plan the timing of the credit, track every leg in both currencies, and report the brokerage account correctly. Therefore, before you open your next short, check which tax year it falls into in each country and whether the accrual election would help.
Contact Us
If you are an American in Britain with open or closed short positions, or with gains that never reached a US or UK return, book a consultation with our cross-border team. You can also email hello@taxyork.com or call 020 3488 8606. We will review your broker statements, quantify any exposure, and prepare compliant returns in both countries.
Disclaimer
This article is for general information only and does not constitute tax, legal or investment advice. Tax rules in the United States and the United Kingdom change frequently, and the correct treatment of any short position depends on your individual facts, residence status and elections. The case study is illustrative, and its figures are rounded. You should obtain professional advice before acting on any information in this article. TaxYork accepts no liability for any loss arising from reliance on this content.