Sold my buy-to-let flat — what exactly is the 60-day CGT rule and what do I need to do?

The 60-day rule is real and it catches most sellers by surprise: when you sell UK residential property that was not your main home — including a buy-to-let — you must report the disposal and pay the Capital Gains Tax due within 60 days of the completion date (not exchange), using a Capital Gains Tax on UK property account. It is a separate filing and payment: you calculate the gain, deduct your annual tax-free allowance and reliefs, apply the residential CGT rates of 18% and 24%, and pay the estimated tax by the 60-day deadline. You then also report the sale on your Self Assessment return for the year — the 60-day return does not replace your tax return, though it is a payment on account toward the final liability. Miss the deadline and interest and penalties apply, so set up the UK property account as soon as completion happens, not weeks later. I have checked the current position on GOV.UK before answering: report and pay within 60 days of completion via the CGT on UK property account remains the live rule.