Already reported a capital gain? Reconcile it before Self Assessment

Bring earlier reports into the annual review

On 28 September 2026, ICAEW reminded people preparing their 2025/26 Self Assessment return to check gains already reported to HMRC and tax already paid. Its warning is practical: missing those details can create complications, including a second charge on the same gain.

For a UK-resident individual completing the Capital Gains Tax summary pages, HMRC’s 2025/26 notes require details of UK property and real-time CGT returns, with the relevant gains or losses also included in the appropriate annual totals. An earlier report should therefore be part of your preparation file.

The workflow below is TaxMirror’s suggested records check. It is not an HMRC checklist or a calculation of your tax.

Create one record for each disposal

Start with the asset and the documents behind its disposal. Link the sale paperwork, cost evidence and gain or loss calculation to a copy of any earlier CGT return. Add the submission reference, submission date and any later amendment.

Keep separate columns for the gain or loss, the tax shown on the earlier return and the payment you can trace. Attach the payment confirmation or relevant bank entry to that last column. A matching number in two columns should not replace a check of what each number means.

Mark the tax year used in the calculation and ask your adviser to resolve any uncertainty about which year the disposal belongs in. Do not assign the tax year solely from the date the payment left your bank.

Distinguish tax charged from cash paid

The tax recorded on an earlier return and the cash you paid answer different questions. Before carrying a figure into Self Assessment, check whether the relevant field asks about tax charged or tax paid. Use HMRC’s 2025/26 notes for the particular reporting route and asset category; avoid treating every field as interchangeable.

For example, your file might contain a property return showing tax due and a bank record showing only a partial payment. Keep both facts visible and flag the difference to your adviser. This example illustrates a records mismatch; it does not decide the annual tax figure or payment obligation.

Keep any explanation of a difference alongside the documents it relies on. If a figure changes during preparation, retain the earlier version and the reason for the change.

Identify which tax payment the record concerns

HMRC’s Agent Update 145, published on 16 July 2026, explains that Self Assessment payments on account are advance payments towards the next bill. Each is typically half the previous year’s bill, excluding Capital Gains Tax and student loan repayments. That distinction matters when you assemble payment evidence: a general Self Assessment payment should not simply be labelled as payment of a particular CGT charge.

Record the service, payment reference, date and amount shown on each confirmation. Link it to the liability you understand it concerns, and flag an uncertain allocation for the preparer to check. Keep this payment trail alongside the earlier CGT return, rather than inferring the allocation from an amount or a bank description alone.

Check the annual entries and exceptions together

HMRC asks for UK property and real-time CGT submission references in box 54. Its notes also provide exceptions to the usual property box treatment where Business Asset Disposal Relief applies. Non-resident disposals have separate instructions. Use the notes for 2025/26 and obtain advice where these circumstances affect you.

In your working file, map each earlier submission to the relevant annual entry and its supporting calculation. Ask the preparer to check the annual totals as well as the fields for previously reported gains and tax. Preserve a copy of the completed return and calculation so the mapping can be followed later.

Before filing, list unresolved items explicitly: a missing submission copy, an unexplained payment difference or a relief question. Give each item an owner and a next action. An unanswered question should remain visible to the person completing the return.