Households continue to spend heavily on home renovations. The UK home-improvement market reached approximately USD 15.0 billion in 2025. Many sellers operate under the assumption that every pound spent on the property will reduce their final tax bill. That belief is financially risky.
Allowable improvement costs for Capital Gains Tax (CGT) are expenses that add lasting value, prolong a home’s life, or adapt it to new uses, such as extensions, new kitchens, or roof replacements. These enhance the property’s base cost to reduce taxable gains. Routine repairs, maintenance, or painting are not deductible.
For the 2026–27 tax year, residential property gains face clear tax rates. Basic-rate taxpayers pay 18%, while higher-rate taxpayers pay 24%. With the annual capital gains allowance sitting at just £3,000, reducing the taxable gain is essential.
HM Revenue & Customs (HMRC) draws a hard line between repairs and improvements. Only one of them reduces your taxable gain. Get this distinction wrong, and you will overpay tax or face a compliance challenge later.
This guide explains exactly what counts as an allowable improvement cost for Capital Gains Tax in the UK.
The Core HMRC Rule You Must Know about Capital Gains
HMRC allows you to deduct certain costs from your capital gain, but the criteria are strict. Improvement costs qualify only if they add value to the property and still exist when you sell.
The work must do at least one of these things:
- Increase the property’s value.
- Extend the property.
- Change the property’s nature or use.
If the work simply keeps the home in good condition, it does not qualify. That single rule dictates the tax treatment of every invoice.
What HMRC Treats as an Allowable Improvement
Allowable improvements change the asset itself. They go beyond maintenance; they create something new or significantly better.
Common examples that usually qualify:
- Building an extension.
- Loft conversions.
- Garage conversions.
- Adding a conservatory.
- Installing central heating where none existed.
- Major kitchen upgrades that improve layout or function.
- Structural alterations.
These costs can reduce your capital gain when you sell, but only if the improvement still exists at the date of disposal.
Repairs vs Improvements: Where Most People Get It Wrong
The distinction between a repair and an improvement is the most common cause of CGT errors. A repair restores an asset to its original state. An improvement upgrades or enhances it.
Repairs do not reduce your capital gain. Examples of repairs that do not qualify:
- Painting walls.
- Fixing roof tiles.
- Replacing broken windows like-for-like.
- Repairing plumbing leaks.
- Replacing damaged flooring with similar material.
Even if these repairs cost thousands of pounds, HMRC ignores them for Capital Gains Tax purposes.
The “Nearest Modern Equivalent” Rule Explained
HMRC accepts that building standards and materials change over time. Replacing an old fixture with a modern version does not automatically classify it as an improvement.
Example: Windows
- Improvement: Replacing old single-pane windows with modern double glazing is usually accepted as an improvement because it significantly enhances energy efficiency.
- Repair: Replacing old double glazing with new double glazing is usually treated as a repair, as the function remains the same.
HMRC looks at function, not just appearance. If the replacement significantly improves efficiency or performance, it may qualify. If it simply restores what existed, it will not.
Mixed Works: How to Apportion Costs Correctly
Renovation projects often include both repairs and improvements.
Example Scenario: You refurbish a kitchen for £15,000.
- £9,000 relates to structural layout changes and added units (Improvement).
- £6,000 relates to repainting and replacing broken tiles (Repair).
In this case, only the £9,000 improvement portion qualifies as a deduction. HMRC allows apportionment, but you must support it with evidence. Your invoices should clearly separate the work types. If they do not, HMRC may disallow the entire claim.
When Improvement Costs Stop Being Allowable
Timing is critical. You cannot claim improvement costs if:
- The improvement was removed before the sale.
- The improvement only benefited personal enjoyment temporarily.
- The work was reversed.
- The work related solely to letting wear and tear (deductible against rental income, not CGT).
Example: You install a luxury bathroom suite but remove it before selling the property. That cost does not qualify because the improvement does not exist at the date of disposal.
A Simple Worked Example in Capital Gains
Understanding the impact of these costs shows why accurate records matter.
- Purchase Price: £240,000
- Sale Price: £420,000
- Gross Gain: £180,000
Allowable Costs:
- Loft conversion: £28,000
- Extension: £42,000
- Legal fees on sale: £4,000
- Total Deductions: £74,000
Result: Your taxable gain becomes £106,000 instead of £180,000. That difference alone can save a higher-rate taxpayer over £17,000 in tax.
What Evidence HMRC Expects You to Keep
HMRC does not accept estimates. They require proof of expenditure.
You must keep:
- Original invoices.
- Contractor contracts.
- Planning permissions.
- Building control sign-off.
- Payment records (bank statements).
- Before-and-after photos.
- Architect or structural drawings.
Absence of paperwork usually results in the deduction being rejected.
Final Thoughts
Capital Gains Tax is not calculated on what you spent; it is calculated on how HMRC categorises that spend. Repairs maintain value; improvements add value. Knowing the difference ensures you keep more of your profit.
If you are unsure how past work should be treated, seek professional advice before you file your return. Once the return is submitted, correcting mistakes becomes a complex process.
Capital Gains Tax Expert can review your renovation history, identify qualifying improvements, and calculate your exact liability. Not sure whether your own improvement costs will qualify? Call us on +44 (0)1204 859315 or use our free CGT calculator to get an instant estimate before you sell.
Questions People Ask – FAQs
- What counts as an allowable improvement for Capital Gains Tax?
Allowable improvements are works that add to the property’s value, extend its life, or adapt it for a new use. Examples include extensions, loft conversions, structural alterations, and permanent upgrades. Routine repairs do not qualify. - Are renovations before selling deductible for CGT?
Only if they meet HMRC’s improvement test. Work done purely to refresh or maintain the home, even if done right before the sale, does not reduce Capital Gains Tax. - Can I claim kitchen or bathroom upgrades as improvement costs?
Sometimes. A full replacement that upgrades the layout or quality may qualify. Like-for-like replacements usually count as repairs and are not allowable. - Do I need receipts to claim improvement costs?
Yes. HMRC expects clear evidence. Invoices, contracts, bank statements, and planning approvals all help support your claim. Missing records often lead to rejected deductions.
5. Can improvement costs reduce Capital Gains Tax years later?
Yes. There is no time limit. As long as the work qualifies and you have proof, HMRC allows you to deduct those costs when you sell, even decades later.
