Home / ISA Calculator

UK ISA Calculator 2025/26

Calculate how your ISA savings could grow tax-free with compound interest. Compare Cash ISA vs Stocks & Shares ISA projections.

Your ISA Details

£
£

Annual: £6,000 (Max allowance: £20,000)

%

Your ISA Projection

Total Value After 10 Years
£92,175.54
+41.8% growth on contributions
Total Contributions
£65,000.00
Interest Earned
£27,175.54
Tax Saved (Est.)
£5,435.11
Effective Rate
7.00%

💰 Contribution Breakdown

  • Initial Deposit £5,000.00
  • Monthly Contributions (×120) £60,000.00
  • Compound Interest +£27,175.54
  • Final Balance £92,175.54

📊 Year-by-Year Projection

See how your ISA grows each year with compound interest

Year Contributions Interest Earned Total Balance

💵 Cash ISA vs 📈 Stocks & Shares ISA

Which ISA is right for you?

Feature Cash ISA Stocks & Shares ISA
Best for Short-term savings, emergency funds Long-term growth (5+ years)
Typical returns 3-5% (variable) 5-10% (historical average)
Risk level Very low - capital protected Medium to high - value can fall
Access to funds Usually instant May take several days
Minimum age 16+ 18+

📚 ISA Jargon Buster

Click on any term to learn more

💰 ISA Allowance ▼
The maximum you can put into ISAs each tax year. For 2025/26, it's £20,000. You can split this across different ISA types, but the total cannot exceed £20,000.
🔄 Compound Interest ▼
Interest earned on both your original deposit AND previously earned interest. This creates a snowball effect - the longer you invest, the faster your money grows. Einstein reportedly called it the "eighth wonder of the world".
🏦 Cash ISA ▼
A tax-free savings account. Interest rates are set by the provider (like a savings account). Your money is protected by the FSCS up to £85,000. Low risk, but returns may not beat inflation.
📈 Stocks & Shares ISA ▼
Invest in funds, shares, or bonds tax-free. Historically returns 7-10% annually over long periods, but value can go down. Best for goals 5+ years away. You can choose index funds for simplicity.
📅 Tax Year ▼
Runs from 6 April to 5 April. Your ISA allowance resets each tax year. Unused allowance doesn't roll over - use it or lose it! Many people rush to use their allowance before 5 April.
🔀 ISA Transfer ▼
Moving your ISA to a different provider. Doesn't count towards your allowance. Important: always use the official transfer process - withdrawing and redepositing uses up your allowance!
🔓 Flexible ISA ▼
An ISA that lets you withdraw and replace money in the same tax year without affecting your allowance. Not all ISAs are flexible - check with your provider. Useful if you might need temporary access.
🏠 Lifetime ISA (LISA) ▼
For first home or retirement. Save up to £4,000/year and get a 25% government bonus (up to £1,000). Must be 18-39 to open. Penalties apply for other withdrawals before age 60.

Why Use an ISA?

ISAs (Individual Savings Accounts) let UK residents save and invest tax-free. All interest, dividends, and capital gains within an ISA are completely exempt from tax.

2025/26 ISA Allowance: £20,000

You can split your allowance between different ISA types:

  • Cash ISA: Tax-free savings account
  • Stocks & Shares ISA: Tax-free investments
  • Innovative Finance ISA: Peer-to-peer lending
  • Lifetime ISA: For first home or retirement (separate £4,000 limit)

Key ISA Rules

  • You must be UK resident and 18+ (16+ for Cash ISA)
  • You can only pay into one of each ISA type per tax year
  • Unused allowance doesn't roll over
  • You can transfer between providers without using allowance
  • Withdrawals don't restore allowance (except flexible ISAs)

The Power of Starting Early

Thanks to compound interest, starting early makes a huge difference. Someone who invests £200/month from age 25 to 65 (40 years) will have significantly more than someone who invests £400/month from age 45 to 65 (20 years) - even though they contributed the same total amount!

⚠️ Disclaimer: This calculator provides projections based on assumed growth rates. Investment returns are not guaranteed and you may get back less than you invest. Past performance is not a reliable indicator of future results. This is for guidance only and not financial advice. Consider seeking independent financial advice.