If you have sold a residential property in the UK and have Capital Gains Tax to pay on the disposal, you must report this to HMRC within 60 days of the completion date and pay the CGT at the same time. The disposal will still be entered onto your self assessment tax return for the year of the disposal.
As CGT is charged at either 18%, 24% or a combination of the two (depending on your other income), calculating the CGT can be challenging, particularly if you have variable income or the sale is early in the tax year.