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ISA Calculator

See how your savings could grow tax-free in a Cash ISA. Every penny of interest you earn in an ISA is yours — no income tax on it. Ever.

Your plan

£
£
%

Best Cash ISA rates are around 4-5% AER (Jul 2026)

After 5 years

£14,731

That's £1,731 in tax-free interest

You put in£13,000
Interest earned£1,731
Tax saved vs regular savings£146

Growth over time

Y1
Y2
Y3
Y4
Y5
Your moneyInterest

💡 Good to know

  • •You can put up to £20,000 into ISAs each tax year (April to April).
  • •Interest in an ISA is completely tax-free — you don't even need to declare it.
  • •Some ISAs are flexible — you can withdraw and replace money in the same tax year without using extra allowance.

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About this calculator

A Cash ISA (Individual Savings Account) lets you save up to £20,000 per tax year and earn interest tax-free. Unlike regular savings accounts where you pay income tax on interest above your Personal Savings Allowance (£1,000 for basic rate, £500 for higher rate), ISA interest is always 100% yours.

This calculator assumes a fixed interest rate and monthly compounding. Actual rates may vary. This is not financial advice — consider speaking to a financial adviser for personalised guidance.

Last updated: July 2026

Frequently asked questions

How much can I put into an ISA each year?
The ISA allowance for 2026/27 is £20,000 across all your ISAs (Cash, Stocks & Shares, Lifetime, Innovative Finance). You can split it however you like, but the total can't exceed £20,000 in a single tax year (6 April to 5 April).
Is ISA interest really tax-free?
Yes — 100% of the interest you earn in a Cash ISA is tax-free. You don't need to declare it on your tax return. Outside an ISA, you'd pay income tax on interest above your Personal Savings Allowance (£1,000 for basic rate, £500 for higher rate taxpayers).
What's the best Cash ISA rate right now?
As of July 2026, the best easy-access Cash ISA rates are around 4–5% AER. Fixed-rate ISAs (where you lock your money for 1–2 years) sometimes offer slightly higher rates. Compare on MoneySavingExpert or bankrate sites.
Can I withdraw money from a Cash ISA?
Yes — most Cash ISAs let you withdraw anytime. If your ISA is 'flexible,' you can withdraw and replace money in the same tax year without using extra allowance. If it's not flexible, any money you put back counts towards your £20,000 limit.