Already paid CGT? Don't pay it twice through Self Assessment

Anyone who made a UK property disposal return or used HMRC's real-time CGT service during the 2025/26 year should check the details before completing the CGT pages of their Self Assessment return.

A UK-resident individual who disposes of UK residential property and has CGT to pay will normally already have reported the disposal and paid an estimate of the tax within 60 days of completion. However, that does not remove the need to include the disposal again in the annual Self Assessment return where one is required.

The return should show both the gain and the CGT previously charged. For UK property disposals, the total gain or loss is entered on the CGT summary pages together with the tax already charged and the reference number for the earlier property return. Similar boxes apply where a disposal was reported using HMRC's real-time CGT service.

This matters because the amount paid through the earlier reporting service is effectively a payment on account of the final CGT liability. If the earlier payment is omitted from the Self Assessment return, HMRC's calculation may not give credit for it correctly and the taxpayer could appear to owe more tax than is actually due.

The final CGT figure can also differ from the amount originally paid. A property return may have been completed before the taxpayer knew their final income for the year or before later capital losses arose, so the Self Assessment calculation effectively brings the position up to date.

Anyone who reported a capital gain separately during 2025/26 should therefore keep the earlier return, payment details and reference number to hand when completing their Self Assessment return. The key is not simply to report the gain again, but also to ensure that credit is given for the CGT already paid.