Free tools / UK capital gains tax and ISA calculator
UK capital gains tax and ISA calculator
See the CGT due on a share sale after the annual exempt amount, and how much of it an ISA would have saved you.
Shares only. Rates and the exempt amount are inputs because both have changed repeatedly; confirm the current tax year figures before filing.
UK capital gains tax on shares is charged only on the part of your gain above the annual exempt amount, at a rate that depends on which income tax band the gain falls into. Inside a stocks and shares ISA the same gain is not taxed at all.
This calculator shows both sides: the tax bill on a taxable account, and the identical position held inside an ISA. The annual exempt amount and the rates are editable, because the allowance has been cut repeatedly in recent years and the rates changed mid-tax-year in 2024.
The allowance has shrunk, so the ISA matters more
The annual exempt amount used to shelter most private investors entirely. After successive cuts it covers only a small gain, which means ordinary portfolios now generate real CGT bills for the first time in years.
The ISA allowance is use-it-or-lose-it: unused headroom does not carry into the next tax year. For a long-term holder, moving new money into the ISA wrapper first is usually the highest-certainty return available, because the saving is guaranteed rather than hoped for.
Which rate applies to you
Gains on shares are taxed at the basic rate if they sit within your remaining basic rate band, and at the higher rate above it. The gain is stacked on top of your income for this test, so a large gain can straddle both rates.
Losses on other disposals in the same year reduce the gain first, and unused losses can be carried forward if you report them. Residential property is taxed at different rates and is out of scope here.
Frequently asked questions
Do I pay capital gains tax inside an ISA?
No. Gains and dividends inside a stocks and shares ISA are free of UK capital gains tax and dividend tax, and you do not report them on a tax return. That is the entire point of the wrapper.
When do I have to report a gain?
You report through Self Assessment, or the real-time service, when your gains exceed the annual exempt amount or your total disposals exceed the reporting threshold. Keeping records of every purchase price matters, because HMRC uses pooled cost rules rather than simple FIFO.
Can I move existing shares into an ISA?
Not directly. You would sell in the taxable account, which itself is a disposal for CGT, and repurchase inside the ISA. This is known as bed and ISA, and the sale may trigger tax even though the holding is unchanged.
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