US UK Tax Returns Preparation: Section 1045 QSBS Rollover

A UK-resident American who sells qualified small business stock early and elects section 1045 reports the sale on Form 8949 with code R, postponing the US gain into the replacement stock. The UK return shows the same sale as an ordinary capital gains disposal, taxed in full in that tax year, with no reinvestment relief.

That asymmetry is why US UK tax returns preparation for a section 1045 year is a two-return exercise rather than a US form-filling task. At Jungle Tax we prepare both sides of these files, and the pattern is consistent: the US election is usually reported adequately, the UK disposal is frequently missed or misdated, and almost nobody has tracked what happens to the UK tax as a foreign tax credit. This guide explains how the election is reported, what the UK return must show for the same transaction, and how the two are reconciled. It is about reporting, not about whether the election should be made.

What is a section 1045 rollover, in return-preparation terms?

Section 1045 of the Internal Revenue Code lets a non-corporate taxpayer elect to postpone gain on a sale of qualified small business stock (QSBS) where the proceeds are reinvested in other QSBS. It exists for the shareholder who sells before reaching the holding period that section 1202 requires for its gain exclusion. It is a deferral, not an exclusion: the postponed gain is embedded in the replacement stock through a basis reduction and surfaces when that stock is eventually sold.

The IRS sets out the conditions in the Instructions for Schedule D (Form 1040). For the preparer, each is a fact to be evidenced on the file:

• The stock sold was QSBS within the section 1202(c) definition: broadly, stock in a domestic C corporation acquired at original issue from a company that was a qualified small business when the stock was issued.
• It was held for more than six months at the date of sale. For this test the holding period is measured without the usual tacking rules.
• Replacement QSBS was purchased during the 60-day period beginning on the date of sale. The count is in calendar days and starts on the sale date itself.
• The taxpayer makes the election by the due date, including extensions, of the return for the year of sale.
• The gain is capital in character. Any part treated as ordinary income is outside the provision.

How much gain is postponed?

The statutory measure is proceeds, not gain. Gain is recognised only to the extent the amount realised on the sale exceeds the cost of the replacement QSBS bought in the window. A shareholder who reinvests the whole of the proceeds postpones the whole gain; one who reinvests only an amount equal to the gain, and keeps the return of original cost, recognises part of it. This is the single most common misunderstanding we correct, and it is the opposite of the UK instinct, where reinvestment reliefs are generally measured by reference to the gain.

How is the section 1045 election reported on Form 8949 and Schedule D?

There is no separate election form. The election is made by the way the sale is reported on the return, following the Instructions for Form 8949:

1. Report the sale as if no election were being made. Enter the description, acquisition date, sale date, proceeds in column (d) and cost basis in column (e), all in US dollars.
2. Use the correct part. Stock held for more than six months but not more than one year is a short-term sale and belongs in Part I; stock held for more than one year belongs in Part II. Several widely read commentaries say a section 1045 sale is always long-term. It is not, and the part chosen determines the rate applied to any gain that is recognised.
3. Tick the box for a transaction not reported on Form 1099-B where, as is usual for private company stock, no broker statement was issued.
4. Enter code R in column (f). If another code applies to the same line, the instructions require all codes to be entered together in alphabetical order.
5. Enter the postponed gain as a negative number, in parentheses, in column (g). Column (h) then shows only the gain that is being recognised, which may be nil.
6. Carry the totals to Schedule D in the ordinary way.

Good practice, and what we do on every file, is to attach a short statement identifying the stock sold, the sale date, the amount realised, the replacement stock, its purchase date and cost, the gain postponed and the resulting basis of the replacement shares. The IRS has published procedural guidance on making the election, and a section 1045 election, once made, can generally be revoked only with IRS consent, so the figures on that statement need to be right first time.

When is the election due for an American living in the UK?

The deadline is the due date of the return for the year of sale, including extensions. A US citizen whose tax home is outside the United States ordinarily has an automatic two-month extension to mid-June and may extend further to mid-October on request. An election on a return filed within the extended period is timely. An election first made on an original return filed after that date is not, which is the point at which catch-up procedures become relevant; we return to that below.

What happens to the basis and holding period of the replacement stock?

Two adjustments follow the election, and both must be recorded in the permanent file because they will not be needed for years.

• Basis. The basis of the replacement stock is its cost reduced by the gain postponed. Where several blocks of replacement stock are bought in the window, the reduction is applied in the order the stock was acquired.
• Holding period. For most purposes the holding period of the replacement stock includes the period for which the original stock was held. That tacked period is what allows a later sale of the replacement stock to be measured against the section 1202 holding period.

The tacking has limits. For the purposes of section 1045 itself, the six-month test on any later rollover is applied to the actual holding period. And the replacement company must satisfy the active business requirement in its own right: section 1045 takes account of only the first six months of the replacement holding for the purpose of qualifying the purchase, but a later section 1202 claim on that stock is tested under section 1202's own rules.

What changed in section 1202 for stock issued after 4 July 2025?

Legislation enacted on 4 July 2025 amended section 1202 for stock acquired after that date. As the statute now reads, the exclusion is phased: 50 per cent of the gain for stock held at least three years, 75 per cent at four years and 100 per cent at five years or more. The per-issuer limitation rises from $10 million to $15 million, with indexation in later years, and the gross assets ceiling for the issuing corporation rises from $50 million to $75 million, a change the Schedule D instructions also record. Stock acquired on or before that date remains under the previous rules.

For a section 1045 file this matters in one specific way: the preparer must record, for every block of replacement stock, the actual acquisition date, the tacked holding period and which version of section 1202 is expected to govern a later sale. How the tacked holding period interacts with the acquisition-date test is a point on which we would confirm the current IRS position before a later exclusion is claimed, rather than assume.

How are partnership and fund purchases reported?

Much angel and early-stage investment is held through partnerships, and the pass-through rules are where reporting errors cluster. In general terms:

• A partnership that sells QSBS and buys replacement QSBS within the window may itself make the election, in which case the partner's share of postponed gain is reflected on Schedule K-1 (Form 1065); the Schedule D instructions direct the partner to the box 11 information on that schedule.
• Where the partnership sells QSBS and does not elect, an eligible partner may be able to make the election on the partner's own return by purchasing replacement QSBS personally within the window, reporting the partner's share of the gain on Form 8949 with code R.
• In either case the benefit is confined to a partner who held the partnership interest for the entire period the partnership held the stock, and is limited by reference to the partner's interest when the stock was acquired.
• A sale of the partnership interest itself is not a sale of QSBS.

The detailed rules sit in the Treasury regulations under section 1045. The practical preparation point is that the K-1 footnotes must be read, because the information needed to make a partner-level election is usually in the supplementary statements rather than on the face of the schedule.

Does state tax follow the federal election?

Not necessarily: a number of states do not conform to the federal QSBS provisions, so a UK-resident American who still has a state filing obligation may have a state gain in the year of sale even though the federal gain is postponed.

What does the UK tax return show for the same sale?

The UK has no equivalent of section 1045. For a UK resident, the sale of the original stock is a disposal for capital gains tax purposes in the UK tax year in which it takes place, and the reinvestment is simply the acquisition of a new asset.

• Timing. The UK tax year runs from 6 April to 5 April. The disposal date under an unconditional contract is generally the contract date, not completion. A sale in the first quarter of a calendar year therefore falls in a different UK tax year from a sale in the second, although both fall in the same US year.
• Sterling computation. The gain is computed in sterling. Proceeds are translated at the rate on the disposal date and the cost at the rate on the original acquisition date. The UK gain is therefore not the dollar gain multiplied by one exchange rate, and can be materially higher or lower than the US figure.
• Share identification. Shares of the same class in the same company are pooled, with same-day and 30-day matching rules applied first. A purchase of shares in a different company does not engage those rules.
• Rate and payment. The gain is charged at the capital gains tax rates in force for that year and the tax is payable by 31 January following the end of the tax year. HMRC's overview is at Tax when you sell shares.
• Base cost of the replacement shares. For UK purposes the replacement stock has a base cost equal to what was actually paid for it, in sterling at the purchase date. The US basis reduction has no UK counterpart.

That last point produces two permanently different cost figures for the same shares, one on each return. A file that carries only one of them will produce a wrong gain in one country when the replacement stock is sold.

Is there any UK relief for reinvesting the proceeds?

Not by virtue of the US election. A cash sale followed by a cash subscription is not a share-for-share exchange, and business asset rollover relief does not apply to shares; that relief, and its own mismatch with US law, is covered in our guide to business asset rollover relief and section 1031. UK tax is deferred only if the replacement shares independently qualify under a UK regime. Enterprise Investment Scheme deferral relief is one such regime, with its own conditions on the issuing company, the investor and the timing of the subscription, described in HMRC helpsheet HS297. It is a different regime from QSBS, and a company meeting one set of conditions will not automatically meet the other.

Section 1045 on the US return and the UK return compared

Point	US return (IRS)	UK return (HMRC)
Is the sale reported?	Yes, on Form 8949 and Schedule D	Yes, on the capital gains pages of the Self Assessment return
Effect of reinvesting in new QSBS	Gain postponed if section 1045 is elected	None
How the relief is shown	Code R in column (f); postponed gain as a negative in column (g)	No entry; no relief exists
What must be reinvested	Proceeds, within 60 days from the sale date	Not applicable
Tax year	Calendar year of sale	Tax year to 5 April in which the disposal falls
Currency	US dollars	Sterling, at the rates on the acquisition and disposal dates
Cost of replacement shares	Purchase cost less postponed gain	Purchase cost in sterling
Holding period of replacement shares	Generally includes the original holding period	Starts on purchase
Deadline	Return due date including extensions	31 January after the tax year for filing online and payment

Why does the foreign tax credit not line up?

A UK-resident American normally relieves double taxation on a gain by crediting the UK tax against the US tax on the same gain. Section 1045 separates the two in time. The UK tax arises now; the US tax, if it arises at all, arises when the replacement stock is sold.

The year of sale: UK tax with little or no US gain

The foreign tax credit is limited, category by category, to the US tax attributable to foreign-source taxable income in that category, computed on Form 1116. If the election postpones the whole gain, there is no US tax on it in the year of sale and the UK tax cannot be used against it. It becomes an excess credit.

Which year the UK tax belongs to depends on the taxpayer's method. On the paid basis it is a credit of the year in which it is actually paid, typically the January after the UK tax year ends. On the accrual basis it is generally a credit of the US year in which the UK tax year ends. Either way it rarely lands in the US year of the sale itself, even before the election is considered.

Carryback and carryforward

Excess credits may be carried back one year and forward ten, within the same category. Capital gains are ordinarily passive category income, but gains bearing foreign tax above the US rate can be moved to the general category under the high-tax rules, so the category must be determined on the facts rather than assumed. The IRS explains the mechanics in Publication 514. The carryforward has to be tracked on a schedule attached to every subsequent Form 1116, whether or not any credit is used that year. A carryforward that is not carried on the returns is, in practice, lost.

The year the replacement stock is sold

When the replacement stock is sold, the US gain includes the postponed gain because of the reduced basis. The UK gain on the same sale is computed from the full sterling cost, so it is smaller, and the UK tax on it may cover only part of the US tax. Three questions then decide whether the old UK tax helps:

• Is the carryforward still alive? If the replacement stock is held for more than ten years after the credit year, it has expired.
• Is the later gain foreign-source? Gain realised by a US citizen with a tax home abroad is not automatically foreign-source; the rules look, among other things, at the level of foreign tax actually paid on that gain. Where the UK tax on the later sale is low relative to the US gain, sourcing, and any treaty-based re-sourcing position, has to be analysed and disclosed properly.
• What do the rate differential adjustments do? Under section 904, foreign-source capital gain taxed at preferential US rates is scaled down when it enters the limitation fraction, and capital losses require their own adjustments. These are computed through the Form 1116 worksheets and can reduce the usable credit well below the headline figure.

If the later sale qualifies for the section 1202 exclusion, the position is different again: the postponed gain may never be taxed in the US, in which case the UK tax paid in the year of the original sale is simply the final cost of the gain and the credits generated by it may go unused. The net investment income tax, where it applies, cannot be reduced by foreign tax credits in any event.

Worked example: one sale, two returns, three tax years

The figures below are hypothetical, rounded and chosen for arithmetic clarity. The exchange rates and tax rates are assumptions for illustration only, not forecasts or current rates.

An American founder resident in London bought QSBS in Company A in March 2024 for $500,000, when the assumed rate was $1 to £0.80. On 1 June 2026 she sells for $3,000,000, at an assumed $1 to £0.75. On 15 July 2026, inside the 60-day period, she subscribes $2,600,000 for QSBS in Company B and elects section 1045.

• US, 2026: realised gain $2,500,000. Proceeds exceed replacement cost by $400,000, so $400,000 is recognised and $2,100,000 postponed. Form 8949, Part II, shows proceeds $3,000,000, cost $500,000, code R, adjustment ($2,100,000), gain $400,000. Basis of Company B stock: $2,600,000 less $2,100,000, or $500,000.
• UK, 2026-27: proceeds £2,250,000, cost £400,000, gain £1,850,000. At an assumed 24 per cent rate, ignoring the annual exempt amount, tax of about £444,000, payable by 31 January 2028. Base cost of Company B stock: £1,950,000.
• Credit position: UK tax of roughly $592,000 at the assumed rate, against US tax on only $400,000 of gain. The large majority becomes an excess credit.

Date	Event	US return	UK return
March 2024	Company A stock acquired	Basis $500,000; holding period starts	Base cost £400,000
1 June 2026	Company A stock sold for $3,000,000	2026 Form 8949: code R, $2,100,000 postponed, $400,000 recognised	2026-27 disposal: gain £1,850,000
15 July 2026	$2,600,000 invested in Company B	Basis $500,000; holding period tacked from March 2024	Base cost £1,950,000; new acquisition
31 July 2026	60-day period ends	No further replacement purchases count	No effect
5 April 2027	UK tax year ends	Accrual basis: UK tax is a 2027 credit, carried back to 2026 then forward	Liability for 2026-27 fixed
October 2027	Extended US due date for 2026	Last date for a timely election	No effect
31 January 2028	UK payment date	Paid basis: UK tax is a 2028 credit, carried back to 2027 then forward	About £444,000 paid
Later year	Company B stock sold	Gain measured from $500,000; section 1202 tested on tacked period	Gain measured from £1,950,000

Notice the carryback. On the paid basis the UK tax is a 2028 credit and carries back only to 2027, missing the 2026 year in which the $400,000 was recognised. On the accrual basis it reaches 2026. The choice of method is a long-term one with consequences beyond this transaction; our role is to compute and present the position accurately under the method the taxpayer is on, and to flag the difference.

What if the election was missed, made late, or reported incorrectly?

These are the catch-up situations we see, in order of frequency.

• Timely original return, election omitted. The Schedule D instructions allow the election to be made on an amended return filed no later than six months after the due date of the original return, excluding extensions, with the statement "Filed pursuant to section 301.9100-2" written at the top.
• Outside that six-month period. Relief is discretionary and is sought from the IRS by a private letter ruling request under the general late-election regulations, which requires the taxpayer to show reasonable and good-faith conduct and no prejudice to the government. It carries a user fee and is not assured.
• Election made, basis never adjusted. The replacement stock is later sold using its full cost, understating the US gain. This is corrected on the return for the later sale, or by amendment if that return has been filed.
• Replacement purchase outside the 60 days, or not QSBS. The election was not valid and the gain belonged in the year of sale. The earlier return needs amending, with interest running from the original due date.
• UK disposal never reported. Often the taxpayer assumed that a deferred US gain meant nothing to report in the UK. The UK return is amended if still in time, or the gain is disclosed to HMRC, with interest and potentially penalties depending on behaviour.
• US returns not filed at all. A UK-resident American who has not been filing may be eligible for the IRS streamlined filing procedures. A section 1045 election cannot be assumed to be available on a delinquent return, because the election has a statutory deadline; the returns generally need to be prepared on the basis that the gain is recognised unless late-election relief is separately obtained, with the UK tax then available as a credit in the ordinary way.

That last scenario is counter-intuitive but often benign: where the UK tax on the sale already exceeds the US tax, recognising the gain in the year of sale with a full credit can leave little or no US tax due, and the replacement stock keeps its full cost as basis.

What records should the file contain?

• Evidence that both the original and replacement stock were QSBS at issue: company representations or certificates, gross asset confirmations and incorporation details.
• Stock purchase and subscription agreements, share certificates or cap table extracts, and bank evidence of each payment with dates.
• A 60-day calculation showing the sale date and each replacement purchase date.
• The election statement and the Form 8949 as filed.
• A basis schedule for the replacement stock showing cost, postponed gain allocated, adjusted US basis and tacked acquisition date.
• A parallel UK schedule showing sterling base cost and the exchange rates used, with their source.
• A foreign tax credit carryover schedule by category and year of origin.
• Schedules K-1 and their footnotes for any holding through a partnership.

These records need to survive until the replacement stock is sold and that return is beyond enquiry in both countries, which may be well over a decade.

How we prepare a section 1045 year

Our work on these files is preparation and compliance. We reconstruct the dollar and sterling computations from source documents, report the election on Form 8949 and Schedule D with a supporting statement, report the disposal on the UK return, build the dual basis schedule, and compute and carry the foreign tax credit position on Form 1116. Where years are missing or an election was mishandled, we prepare the amended or delinquent returns and the disclosure to HMRC. Founders weighing the wider exit position will find the section 1202 and Business Asset Disposal Relief interaction in our founder exit guide; this page is confined to reporting the rollover.

Our US tax return and UK Self Assessment teams work from one file, which is the only reliable way to keep two bases, two currencies and two tax years aligned. You can read more about how our US-UK tax accountants work with founders and investors.

If you have sold qualified small business stock while resident in the UK, or have a section 1045 election in an earlier year that was never matched on the UK side, we can review the position and tell you plainly what each return should show. Please contact our cross-border team to arrange a confidential consultation; we will examine the sale, the reinvestment and the filing history in both countries before any work begins.