Calculate the future value of your Individual Savings Account (ISA), including tax-free growth from regular contributions.
2025/26 annual ISA allowance (example)
An ISA calculator projects how your Individual Savings Account (ISA) balance could grow over time from an initial deposit and regular monthly contributions, with all growth shown as entirely tax-free — reflecting the core benefit of the ISA "wrapper" itself, regardless of whether the underlying ISA is cash, stocks and shares, or another type.
This calculator compounds your balance monthly at the entered growth rate, adding your monthly contribution each month. Because all growth within an ISA is tax-free, the full compounded amount — including all interest, dividends, or investment gains — is yours, with no further tax to pay, regardless of how much the account grows.
Formula: Each month, Growth = Balance × (Annual Rate ÷ 12); Balance = Balance + Growth + Monthly Contribution. This repeats for the number of months entered. Total Growth = Final Balance − Total Contributions (Initial Deposit + sum of all monthly contributions).
Example: Starting with a £5,000 deposit and contributing £500/month at an expected 5% annual growth rate (example rate — enter a rate appropriate to your ISA type) over 10 years, total contributions reach £65,000 (£6,000/year, well within the £20,000 annual ISA allowance), with total tax-free growth of around £20,876 — giving a final tax-free ISA balance of roughly £85,876. (Note: this example is for illustration purposes only — actual returns depend on your ISA type and investment performance.)
An Individual Savings Account (ISA) is a tax-efficient "wrapper" that shields savings and investments from Income Tax and Capital Gains Tax — there's no tax to pay on interest, dividends, or gains within an ISA, no matter how large the balance grows or how much you withdraw. Each tax year, there's an annual ISA allowance (£20,000 for the 2025/26 tax year, example — check the current allowance) that you can split across different types of ISA as you wish: Cash ISAs (similar to a savings account but tax-free), Stocks & Shares ISAs (investments held tax-free, with the potential for higher growth but also investment risk), Innovative Finance ISAs (peer-to-peer lending), and the Lifetime ISA (with its own £4,000 annual sub-limit and government bonus — see our separate Lifetime ISA calculator for that specific product). Unused ISA allowance doesn't carry over to the next tax year — it's a "use it or lose it" allowance that resets each 6 April. Many ISAs are also "flexible," meaning you can withdraw money and replace it within the same tax year without it counting twice against your allowance — check whether your specific ISA provider offers this. Given the tax-free status, ISAs are generally a sensible first home for savings and investments before considering taxable accounts, up to the annual allowance.
For the 2025/26 tax year, the annual ISA allowance is £20,000 (example — check the current allowance, as this is reviewed periodically). This is the total amount you can pay into ISAs across all types in a single tax year, combined — it's not £20,000 per ISA type.
A Cash ISA works like a tax-free savings account, paying interest with no tax to pay, similar in structure to a regular savings account but without the interest counting toward your Personal Savings Allowance. A Stocks & Shares ISA holds investments (such as funds, shares, or bonds) within the tax-free wrapper — potential returns can be higher over the long term, but the value can fall as well as rise, unlike a Cash ISA.
No. The ISA allowance resets each tax year (starting 6 April) and any unused portion is lost — it cannot be carried forward. This is why many people aim to use as much of their allowance as they can afford each year, if tax-efficient saving is a priority.
A flexible ISA allows you to withdraw money and pay it back in within the same tax year without the replaced amount counting again against your annual allowance. Not all ISAs are flexible — check with your provider whether this feature applies to your specific account.
Yes — interest, dividends, and capital gains within an ISA are free from Income Tax and Capital Gains Tax, regardless of how large your ISA balance grows or how much you've contributed over the years. This is the core benefit of the ISA wrapper compared to holding the same investments or savings outside an ISA.
For most people, using available ISA allowance before holding equivalent investments in a taxable account makes sense, since ISA growth is entirely tax-free, whereas taxable accounts may incur Income Tax (on interest/dividends above your allowances) or Capital Gains Tax on gains. However, your personal circumstances, other tax allowances, and investment goals should guide this decision — consider speaking with a financial adviser for personalised guidance.
Disclaimer: The information, rates, and allowances provided on this page are for educational and illustrative purposes only and do not constitute financial or tax advice. The annual ISA allowance and tax rules are set by the government and reviewed periodically, and may have changed since this page was published. The growth rate used is an example only and does not represent a guaranteed or likely return for any specific ISA product — investment values can fall as well as rise. Always check current allowances and rules, and consult a qualified financial adviser before making investment decisions.