Capital Gains Tax Calculator — What You'll Actually Owe

Capital Gains Tax (CGT) is the tax charged on the profit — not the total sale price, just the gain — when you sell or otherwise dispose of an asset that's gone up in value. Common triggers include shares held outside an ISA or pension, a second home or buy-to-let property, cryptoassets, and valuable possessions above certain thresholds.

This is genuinely the single most common misunderstanding worth clearing up first: if you sell shares for £20,000 that originally cost you £12,000, you're not taxed on the £20,000 — you're taxed on the £8,000 gain, and even then, only on the portion above your annual allowance.

Every individual gets an annual exempt amount (AEA) — a slice of gains you can make each tax year completely tax-free. For 2026/27, that's £3,000 — a quarter of what it was just three years ago.

That reduction means far more people now have a genuine CGT liability than in previous years — even a modest share portfolio or a small buy-to-let sale can trigger a taxable gain today that would have been completely covered by the allowance a few years ago. The AEA cannot be carried forward: if you don't make any gains in a given tax year, that year's £3,000 allowance is simply lost, not banked for later.

Since the October 2024 Budget, CGT applies a single, unified rate structure across almost all asset types — shares, funds, crypto, and residential property are all taxed the same way, ending the previous split where property carried a higher rate than shares.

Your gain stacks on top of your other taxable income for the year to decide which band applies — this is the detail that catches people out most often. If your income plus the taxable gain stays within the basic-rate band (up to £50,270 of total income), you pay 18%. Cross that threshold, and the portion of the gain above it is taxed at 24%, even if you'd normally think of yourself as a basic-rate taxpayer based on salary alone.

Working through a capital gains tax on property calculator matters more than for most other assets, because of a strict deadline. If you sell a UK residential property that doesn't qualify for full Private Residence Relief — a buy-to-let, an inherited home, a holiday cottage — you can't simply wait until the end of the tax year to sort out CGT the way you can with shares. You must report the sale and pay an estimate of the tax to HMRC within 60 days of completion. Miss this window and penalties can apply, on top of the tax itself.

This genuinely trips people up, because it runs on a completely different timeline from Self Assessment. Build it into your plan the moment a property sale completes, not months later when your accountant asks about it.

Your only or main residence is exempt from CGT under Private Residence Relief, in almost all normal circumstances — this is why most people never think about CGT at all when they sell the house they actually live in. This relief can be reduced or lost, though, if you've let part or all of the property out, used a significant portion for business purposes, or own more than one property without correctly nominating which is your main residence for tax purposes. If any of those apply to you, it's worth getting specific advice rather than assuming the exemption automatically covers the whole gain.

Transfer assets between spouses or civil partners tax-free before selling. Since these transfers don't trigger CGT, moving an asset to a partner in a lower tax band — or simply making an asset jointly owned — can effectively double your combined allowance to £6,000 and shift some of the gain into a lower rate band.

Split a large disposal across two tax years where genuinely possible, to use two separate £3,000 annual exempt amounts rather than one.

Offset losses from other asset sales in the same year — losses reduce your gain before the allowance is applied, and unused losses can generally be carried forward to future years (unlike the allowance itself).

You bought a buy-to-let property for £200,000. You sell it for £260,000, after £8,000 of selling and legal costs. Your gain: £260,000 − £200,000 − £8,000 = £52,000.

Subtract the £3,000 annual exempt amount: taxable gain of £49,000. As a higher-rate taxpayer with other income already above £50,270, the entire taxable gain falls in the higher band, taxed at 24%: £49,000 × 24% = £11,760 owed to HMRC, reportable and payable within 60 days of completion.

Now picture the same property held jointly with a spouse. Each of you has your own £3,000 allowance, so £6,000 of the gain is tax-free instead of £3,000, and if your spouse is a basic-rate taxpayer, their half of the gain is taxed at 18% rather than 24% — a meaningfully lower combined bill for identical proceeds, purely from how ownership was structured.

Official sources & further reading: check current CGT rates and rules at GOV.UK, read general tax guidance at MoneyHelper, and confirm your position with a qualified accountant. Model your ISA-sheltered alternative with our ISA calculator, or browse every tool on the mortgage calculators homepage.