How to report ETF and share sales on the SA108 capital gains pages

1. Do you need the capital gains pages at all?

The SA108 notes for 2025–26 (the “Capital Gains Tax summary” pages of the Self Assessment return) say to fill them in if, among other cases:

• you sold or disposed of chargeable assets worth more than £50,000;
• your chargeable gains before taking off any losses were more than £3,000 (the annual exempt amount);
• you want to claim an allowable capital loss, or make a capital gains claim or election for the year.

The first test catches many long-term investors: rebalancing £60,000 of funds at a small gain still needs the pages.

Two kinds of account stay out. The same notes say you do not need the pages if you only dispose of stocks and shares held in tax-free savings accounts such as ISAs and PEPs. And gains on investments held for a registered pension scheme, such as a SIPP, are not chargeable gains (TCGA 1992 s.271(1A)). Everything below is about your general (taxable) dealing accounts.

2. Step 1: match each sale to the shares it came from

UK rules do not use first-in, first-out. Shares of the same class in the same company — or units of the same ETF share class — are matched in a fixed order. HMRC’s helpsheet HS284 sets it out:

1. Same day. Shares bought on the same day as the sale (TCGA 1992 s.105).
2. The next 30 days. Shares bought in the 30 days after the sale, earliest first (s.106A(5)) — the “bed and breakfast” rule. HS284 adds the condition that you were UK resident when you bought; s.106A(5A) sets out the exception.
3. The Section 104 holding. Whatever is left comes from the pool of everything else you hold, at its average cost (s.104 treats those shares as a single asset).

Three consequences matter in practice:

• Selling at a loss and buying back within 30 days does not give you a loss against the old cost: the sale is matched with the new purchase instead.
• Only purchases you make in your own taxable accounts count. Buying back inside an ISA or a pension is outside these rules, which is why “bed and ISA” crystallises the gain or loss.
• Shares matched under rule 1 or 2 never enter the Section 104 holding, so the pool’s average cost is not changed by them.

The allowable cost of a sale is the cost the matching gives, plus your incidental costs of selling, such as the broker’s commission (TCGA 1992 s.38 lists agents’ fees and commission). The purchase commission is already inside the cost.

3. Step 2: convert every amount at its own date’s rate

For shares bought or sold in dollars or euros, HMRC’s Capital Gains Manual (CG78310) says the cost is the sterling equivalent at the exchange rate on the date of acquisition, and the proceeds the sterling equivalent on the date of disposal — the principle confirmed in Bentley v Pike. HMRC does not prescribe a reference rate, but expects a reasonable and consistent method.

So you do not work out a gain in dollars and convert it once. Each purchase goes into the pool at its own day’s rate, and the proceeds at the sale day’s rate. The currency movement is part of the gain — and a dollar gain can be a sterling loss, as the example below shows.

4. Step 3: add excess reportable income to the cost of offshore funds

Most ETFs UK investors buy are domiciled in Ireland or Luxembourg, which makes them offshore funds. HMRC’s helpsheet HS265 divides them in two:

• Reporting funds. You are taxed each year on your share of the fund’s reported income, whether or not it is paid out. The part not distributed — excess reportable income (ERI) — is treated as received on the fund distribution date, six months after the end of the fund’s reporting period, and declared as income. For an accumulating fund, that can be all of the income.
• Non-reporting funds. A gain on disposal is normally an offshore income gain, taxed as income rather than as a capital gain (HS265). HMRC publishes a list of reporting funds; the fund manager can also confirm the status.

Because ERI has already been taxed as income, HS265 says it can be deducted when calculating your capital gain, so it is not taxed twice. In practice this means adding it to the cost of the units you held at the end of each reporting period. Miss it on an accumulating ETF held for a decade and you overstate the gain by every year’s ERI.

HS284 makes the same point for accumulation units in general: notional distributions charged to income tax count as additional expenditure on the units.

5. A worked example

Illustrative figures only: the fund, prices, exchange rates and ERI per unit are made up to show the method. They are not data for any real fund.

Sam holds an accumulating Irish ETF (a reporting fund) and one US share in a general account. In the 2025–26 tax year:

Disposal A: 300 units of the ETF on 10 January 2026

The 300 units sold are matched in order:

Without the ERI the pool cost would be £80.00 a unit and the gain £75 higher. After the sale the Section 104 holding is 250 units at £20,125; the 150 units bought in January are not in it.

Disposal B: 20 US shares on 3 March 2026

A $240 gain in dollars is a £100 loss in sterling, because the pound strengthened while Sam held the shares. The sterling figure is the one that counts.

6. Step 4: the totals the SA108 asks for

The 2025–26 SA108 form (the version headed “Tax year 6 April 2025 to 5 April 2026”) has a section headed Listed shares and securities. The notes define it as shares or securities of a company listed on a recognised stock exchange, shares in a UK open-ended investment company and units in an authorised unit trust; AIM shares and some relief cases go in the unlisted section instead. Most exchange-listed ETFs held by individual investors are shares of a listed company or units of a listed fund, but check the notes against what you hold. The boxes, named as the form names them:

Points from the notes worth knowing:

• Box 23: count all disposals of the same class of share in the same company made on the same day as a single disposal.
• Box 24: total proceeds before taking off any reliefs, claims or elections.
• Box 26 and 27 are separate: gains are not netted against losses on the form itself.
• Boxes 28 to 30 are for claims or elections and for gains already reported through the “real time” Capital Gains Tax service; most portfolio investors leave them empty.
• Losses brought forward from earlier years go in box 45, in the “Losses and adjustments” section, and the notes say they can only reduce gains down to the annual exempt amount.
• The form says you must enclose your computations, including details of each gain or loss, as well as filling in the boxes. That is the per-sale list from Step 1.

7. Step 5: the annual exempt amount

The annual exempt amount for individuals is £3,000 for 2024–25, 2025–26 and 2026–27, per gov.uk’s Capital Gains Tax rates and allowances (updated 13 April 2026). The same page gives the rates for individuals: most gains at 18% or 24%, depending on your taxable income.

Sam’s net gain is £5,070 − £100 = £4,970, which is £1,970 above the exempt amount. You do not deduct the exempt amount in the boxes yourself; HMRC’s calculation does that.

8. How Borderfolio helps

With the United Kingdom set as your tax residence, the tax page of the investor app has a card called Disposals for your capital gains pages. It is built from the confirmed transactions you imported from your broker statements, across your general accounts:

• Every sale in the tax year (6 April to 5 April), with its proceeds, cost, costs of selling, allowable cost and gain, and the rule that matched it — for example “50 same day · 100 next 30 days · 150 Section 104 holding”.
• Each amount in sterling at its own trade date’s rate.
• Excess reportable income added to cost where the issuer’s report is in our catalogue and you still hold the fund; the amount included is shown on each sale.
• The year’s totals — net gain (gains and losses separately), disposal proceeds, allowable costs — and the part above that year’s annual exempt amount.
• A CSV with one line per disposal and a totals line, to keep with your computations or send to your accountant.

Free shows the totals; the per-sale list and the CSV are part of Pro ($15 a month or $149 a year). It lists what the capital gains pages ask for. It does not fill in or file the form.

What it does not cover, as the card itself says:

• ISAs and pensions are left out, by design.
• Shares bought before your imported history, or transferred in without a cost, have no cost and are listed as unknown; totals are then left empty rather than guessed.
• Corporate actions not on file (takeovers, share exchanges, spin-offs, return of capital) are not reflected; splits on file are.
• A separate gain on foreign currency itself, such as cash held in dollars, is not computed.
• Losses brought forward from earlier years, losses on other assets and gains outside these accounts are not on file.
• Joint accounts are listed in full; your share of a joint disposal is not split out.

The same UK checks also list the excess reportable income to declare as income, and each offshore fund’s reporting status from HMRC’s list.

FAQ

Do I need the SA108 if my gains are below £3,000?

Possibly. HMRC’s SA108 notes for 2025–26 say to fill in the capital gains pages if you disposed of chargeable assets worth more than £50,000, if your gains before losses were more than £3,000, or if you want to claim an allowable loss, among other cases. A year of small gains on large sales can still need the pages.

Do sales inside an ISA or a SIPP go on the SA108?

No. The SA108 notes say you do not need the pages if you only dispose of stocks and shares held in tax-free savings accounts such as ISAs and PEPs, and TCGA 1992 s.271(1A) exempts gains on investments held for a registered pension scheme. Buying back inside an ISA also does not count for the 30-day rule on a sale in a general account.

Which exchange rate do I use for US shares?

Each amount at the rate of its own date: the purchase at the rate on the day you bought, the proceeds at the rate on the day you sold (CG78310). HMRC does not prescribe a reference rate but expects a reasonable and consistent one. The currency movement therefore ends up inside the gain or loss.

Does Borderfolio fill in my SA108?

No. It lists the disposals in your general accounts for a tax year, the rule that matched each sale, and the totals the capital gains pages ask for, against the annual exempt amount. You enter the figures yourself or give the list and CSV to your accountant. It is an estimate from your own data, not tax advice.