For a UK resident selling UK residential property, Capital Gains Tax due on the sale generally has to be reported and paid within 60 days of completion. Non-residents have wider reporting rules. Tell the accountant the completion date immediately; the annual return deadline may be too late.
The completion date starts the urgent check
Tell the accountant when the sale completes, even if the full cost paperwork is not ready. For a UK resident disposing of UK residential property with Capital Gains Tax due, the reporting and payment deadline is generally 60 days from completion. Check non-resident reporting separately because it can apply more widely.
The mortgage balance is not the gain
The amount left in your bank after repaying a mortgage is not the tax calculation. Gather the purchase and sale statements, relevant costs, ownership shares and any relief information. Financing and capital gain are different calculations.
Prepare the property’s history
- Purchase, sale and completion dates.
- Periods it was your home, let or used differently.
- Changes in ownership and residence abroad.
- Evidence of qualifying improvements and transaction costs.
Give real dates rather than “a few years ago”. Those facts can affect relief and reporting.
Confirm the separate report and annual return
A 60-day property report and an annual return can both be relevant. Ask who is responsible for each and whether the work is included in the fee. Do not assume a standard rental-income return package includes a property disposal calculation. Contact TaxSimba with the completion date and ask it to confirm the appropriate support.
Count from legal completion, then prepare the report
If completion is 20 October 2026, 60 calendar days later is 19 December 2026. That illustrates the date calculation only; first establish that the reporting rule applies. Use the date tool below and allow time to prepare and pay.
The official UK-property reporting route explains account setup and the information required. Where Self Assessment also applies, include the disposal there and account for tax already paid through the property report. Do not count that earlier payment twice.
Completion date starts a separate clock
Illustrative example.
In a fictional sale completed on 1 October 2026, adding 60 days gives 30 November 2026. If the disposal is within the residential-property reporting requirement, the relevant report and payment cannot simply wait for the usual annual-return timetable. The example assumes no special circumstances.
Tell the accountant immediately, even if one invoice is missing. Provide purchase and disposal details, ownership shares and occupation history so the actual reporting requirement and calculation can be checked. A mortgage settlement statement alone does not establish the gain.
| Check | Practical action |
|---|---|
| Completion | Record the actual date, rather than the estate-agent listing date. |
| Calculation inputs | Provide acquisition, disposal, costs, ownership and relief information. |
| Separate tasks | Confirm property reporting, payment and any annual-return entry. |
Does each joint owner report the whole gain?
Give the accountant the ownership details. Each owner’s reporting position needs checking; do not duplicate the full proceeds as each person’s own disposal.
Can I wait until I have every document before mentioning the sale?
Alert the accountant immediately and list the missing records. That allows the deadline and next steps to be addressed promptly.
Download a checklist for this guide
- Completion and exchange dates
- Purchase and sale statements
- Ownership shares and residence history
- Fees, improvements and relevant relief evidence
- Property report, payment and annual-return responsibilities