Property Capital Gains Tax is not just a sale price minus purchase price calculation. The result can move because of reliefs, allowable costs, losses, income bands and reporting deadlines.
Use the CGT Calculator if you want to build a residential property estimate from your own sale figures.
Start on the sale-tax route
Property CGT becomes confusing when purchase costs, SDLT and rental cash flow are pulled into the same answer. Use the route that matches the decision:
| If the question is… | Best route | Why |
|---|---|---|
| ”What CGT might I owe if I sell?” | CGT Calculator | It models the gain, reliefs, losses, annual exemption and residential property rate split. |
| ”Which CGT rules change the result?” | Keep reading this guide | Relief, allowable costs and reporting deadlines need context before the estimate is trusted. |
| ”Should I sell or keep the rental?” | Buy-to-Let Calculator | The disposal decision should be compared with ongoing yield and mortgage cost. |
| ”What tax applies when I buy the next property?” | Stamp Duty Calculator | SDLT is a purchase tax and should be calculated separately from the sale gain. |
| ”How much cash do I need for the next purchase?” | Fees and Costs Calculator | Legal, survey, lender and moving costs belong to the next purchase budget, not the CGT computation. |
When property CGT usually matters
Residential property CGT is most likely to matter when selling:
- a buy-to-let property
- a second home
- a former main home that was rented out or used differently for part of the ownership period
- a property where only part of the gain qualifies for main-home relief
It is less likely to matter where the property was your only or main home throughout ownership and full Private Residence Relief applies.
The core calculation
The broad calculation is:
- start with the sale proceeds
- deduct the purchase price
- deduct allowable buying, selling and capital-improvement costs
- apply any relevant relief, such as Private Residence Relief
- deduct allowable capital losses
- apply the annual exempt amount
- split the remaining taxable gain across the relevant CGT rates
The rate question comes late in the process. If the gain is overstated at the beginning, the tax estimate will be wrong before the rate is even applied.
Current residential property rates
For individual residential property gains in 2026/27, the calculator uses:
| Part of gain | Rate |
|---|---|
| Amount falling within the unused basic-rate band | 18% |
| Amount above that band | 24% |
The annual exempt amount is £3,000 for 2026/27.
That is why taxable income matters. A basic-rate taxpayer can still have part of a gain taxed at 24% if the gain pushes the combined amount above the basic-rate band.
Private Residence Relief is the first big boundary
Private Residence Relief can remove the gain where the property was your only or main home throughout ownership.
Where the property was your home for only part of the time, the calculation can become more nuanced. The period lived in as the main home, final-period relief and any non-qualifying use can all affect the taxable gain.
This is the point where a former home should not automatically be treated like a pure buy-to-let sale.
Allowable costs need careful separation
Common cost categories to check are:
- buying costs that are allowable for CGT
- selling costs that are allowable for CGT
- capital improvements that add to the property
- allowable capital losses
Routine repairs and maintenance do not become capital improvements simply because they were expensive. That boundary is one of the places where a quick estimate can drift.
The 60-day reporting point
Where residential property CGT is due, the reporting and payment window is usually 60 days from completion.
That deadline matters because a sale can create a tax task before the next Self Assessment cycle. The calculator helps estimate the number, but the reporting route and payment timing still need to be handled properly.
When the calculator is not enough
Get fuller tax advice where the sale involves:
- trusts, companies or non-resident ownership
- mixed-use property
- several disposals in the same tax year
- uncertain main-home history
- improvements and repairs that are hard to separate
- losses from other assets that need to be coordinated
The CGT Calculator is designed for ordinary residential property modelling. It should not flatten specialist ownership or reporting situations into a single answer.
Where to go next
- Use the CGT Calculator to estimate the residential property gain.
- Use the Buy-to-Let Calculator if you are deciding whether to sell or keep a rental property.
- Use the Stamp Duty Calculator if the sale feeds into a replacement purchase.
- Use the Fees and Costs Calculator only for the buying-cost side of the next transaction.