How to Report Capital Gains on Shares: Real Time Service or Self Assessment (2026/27)

Sold shares at a gain? When you must report to HMRC, how to use the real time CGT service or Self Assessment, and how to match shares - step by step.

2026/27 tax year

Capital Gains
Investor
UK-wide

Summary

You must report and pay Capital Gains Tax on shares if your total taxable gains for the tax year, after losses, are above the £3,000 tax-free allowance for 2026/27.
If you are registered for Self Assessment you must also report on your return when the total you sold assets for was more than £50,000, even if your gains are under the allowance.
UK residents can use HMRC's real time Capital Gains Tax service instead of a tax return: report by 31 December after the end of the tax year and pay by 31 January, so a 2026/27 gain is reported by 31 December 2027.
Before you calculate a gain, match the shares you sold in HMRC's order: shares bought the same day, then shares bought in the following 30 days, then the Section 104 pool at average cost.
Shares held in an ISA or PEP are outside Capital Gains Tax, and so are gains on investments held for a registered pension scheme.

This guide is general information, not advice.

This guide is for anyone who sold, gave away or swapped shares, unit trusts or funds held outside an ISA or pension and needs to tell HMRC. It covers the procedure: whether you have to report, which of HMRC’s two routes to use, how to match the shares you sold, and what to keep.

By the end you will have a matched gain figure, a written calculation you can attach or keep, and a reporting deadline. For the rates themselves, and how gains stack on top of income, see the CGT 2026/27 guide.

Before you start

Check the shares are chargeable. GOV.UK lists shares not in an ISA or PEP, units in a unit trust and certain bonds. You do not pay Capital Gains Tax when you dispose of shares in an ISA or PEP, shares in an employer Share Incentive Plan, UK government gilts or Qualifying Corporate Bonds. Gifts of shares to a spouse, civil partner or charity are usually tax-free. HMRC’s Pensions Tax Manual confirms that gains on investments held for a registered pension scheme, such as a SIPP, are exempt.

Check whether you have to report. Per GOV.UK, add up the gains on everything you disposed of in the tax year and deduct allowable losses. You report and pay if the result is above the tax-free allowance, which is £3,000 for 2026/27. If you are registered for Self Assessment, you must also report on your return if the total you sold assets for was more than £50,000, even when your gains are under the allowance.

Have ready:

contract notes or broker statements for every purchase and sale of that company’s shares, not only this year’s
dates of each purchase and sale
dealing costs: GOV.UK lets you deduct fees such as stockbrokers’ fees and the Stamp Duty Reserve Tax you paid when you bought
your HMRC sign-in details (GOV.UK says you can create them the first time you sign in), and your UTR if you are in Self Assessment
your expected taxable income for the year, which sets the rate

Step-by-step

List every disposal in the tax year. Selling is not the only disposal: GOV.UK includes giving an asset away and swapping it. For a gift to anyone other than a spouse, civil partner or charity, use the market value on the date of the gift.
Match the shares sold. Shares of the same class in the same company are identical, so HS284 sets the order. Shares you sold are matched with:
- first, shares acquired on the same day as the sale
- second, shares acquired in the 30 days following the sale, provided you were UK resident when you bought them
- third, shares in your Section 104 holding, a single pool where every share carries the same average cost
Work out the gain for each matched part. For the 30-day part, the gain is the apportioned proceeds minus what you paid for the new shares. For the pool part, the allowable cost is the pool cost multiplied by shares sold divided by shares in the pool. Reduce the pool by the same fraction and carry the remainder forward.
Total your gains and losses. Deduct losses of the same year first. GOV.UK says you then use earlier unused losses only to bring the total down to the allowance, carrying the rest forward.
Choose your route. Per GOV.UK:
- Real time Capital Gains Tax service. For disposals in 2025/26 or 2026/27. You must be UK resident and reporting for yourself. It cannot be used for UK residential property, foreign tax credit relief on overseas property, or life insurance chargeable event gains. You must attach a copy of your calculations. Start from the GOV.UK page above and sign in.
- Self Assessment. Enter the gains on the Capital Gains summary pages, SA108, of the return for the tax year after the sale. HMRC then tells you what you owe.
If you are already registered for Self Assessment and use the real time service, GOV.UK says you must still include the sale on your tax return.
Pay with the right reference. After a real time report, HMRC sends a letter or email with a payment reference starting with X. Use it with HMRC’s online payment service, bank transfer or cheque. Gains reported through Self Assessment are paid as part of your Self Assessment bill.
Correct a mistake if needed. For the real time service, GOV.UK says you submit a new report quoting the reference starting with RTT that HMRC emails you after first use.

Deadlines and what happens next

Real time service: report by 31 December in the tax year after the gain and pay by 31 January. GOV.UK’s example: a 2025/26 gain is reported by 31 December 2026 and paid by 31 January 2027. Applying the same rule, a 2026/27 gain is reported by 31 December 2027 and paid by 31 January 2028.
Self Assessment: per GOV.UK, if you have never sent a return, or did not need to send one for the previous year, you must tell HMRC by 5 October after the tax year ends, so by 5 October 2027 for 2026/27. The online return and the payment are due by 31 January, which for 2026/27 is 31 January 2028.
Losses: you can claim up to 4 years after the end of the tax year of the disposal, per GOV.UK. If you have never made a gain and are not in Self Assessment, you can write to HMRC instead.
Records: keep them for at least a year after the Self Assessment deadline, longer if you filed late or HMRC opens a check, per GOV.UK record keeping. Keep your pool working too: it sets the cost of every future sale.

Common mistakes

Using average cost when you bought back within 30 days. The 30-day match comes before the pool, and those repurchased shares never join it.
Ignoring the £50,000 proceeds test. If you are in Self Assessment, a gain under the allowance can still need reporting.
Forgetting disposals that are not sales. Gifts to children and share swaps count, at market value where GOV.UK says so.
Reporting only, not paying. The X reference is how HMRC matches your payment; a wrong reference can land it on a different tax bill.
Using the real time service for a flat or for an estate. Residential property goes through the 60-day UK property account, and shares sold by an estate are reported with the estate.

Worked example

All figures are illustrative; the allowance and rates are the 2026/27 figures from GOV.UK.

You hold shares in one company: 1,000 bought for £4,000 and 1,000 bought later for £6,000. Your Section 104 pool is 2,000 shares costing £10,000.

On 10 June 2026 you sell 1,500 for £12,000 after dealing costs. On 25 June 2026, fifteen days later, you buy 500 back for £3,800.

Matched part	Shares	Proceeds	Cost	Gain
30-day rule (25 June purchase)	500	£4,000 (500 ÷ 1,500 × £12,000)	£3,800	£200
Section 104 pool	1,000	£8,000	£5,000 (1,000 ÷ 2,000 × £10,000)	£3,000
Total	1,500	£12,000	£8,800	£3,200

Total gains of £3,200 exceed the £3,000 allowance, so you must report even though proceeds are well under £50,000. The taxable gain is £200: £36 at 18% if it falls inside your unused basic-rate band, £48 at 24% if not.

Your pool carries forward as 1,000 shares costing £5,000. The 500 bought on 25 June were used up by the 30-day match. Using the real time service, you report by 31 December 2027, attach this table, and pay by 31 January 2028.

Capital Gains Tax 2026/27 - rates, reliefs and how gains stack on income.
CGT on shares calculator - run your own pool figures, or the general capital gains tax calculator.
How to report and pay CGT on a UK property within 60 days - the separate route for residential property.

Frequently asked questions

Do I have to report selling shares if my gain is under £3,000?

Usually not, because you only pay Capital Gains Tax on total taxable gains above the £3,000 allowance for 2026/27. But GOV.UK says that if you are registered for Self Assessment you must still report your gains on your tax return if the total amount you sold the assets for was more than £50,000. Losses follow separate rules: you report them to use them.

What is the real time Capital Gains Tax service?

It is an online HMRC form for reporting gains without waiting for a tax return. GOV.UK says it covers disposals in 2025/26 and 2026/27, you must be UK resident, and you cannot use it for UK residential property or for someone else. You report by 31 December after the tax year ends and pay by 31 January using the payment reference starting with X that HMRC sends you.

What is the deadline to report a capital gain on shares sold in 2026/27?

Through the real time service, 31 December 2027, with payment by 31 January 2028. Through Self Assessment, the online return and payment are due by 31 January 2028, and if you have never sent a return you must tell HMRC by 5 October 2027 that you need one. These follow the rules GOV.UK states for each route.

How do the 30-day and same-day rules work for shares?

HMRC's helpsheet HS284 says shares you sell are matched first with shares of the same company and class bought on the same day, then with shares bought in the 30 days after the sale, and only then with your Section 104 pool at average cost. The 30-day rule applies only if you were UK resident when you bought the new shares.

How long do I have to claim a capital loss on shares?

GOV.UK says you can claim up to 4 years after the end of the tax year in which you disposed of the asset. You claim on your tax return, or by writing to HMRC if you have never made a gain and are not registered for Self Assessment. Losses are set against gains of the same year first.