Free UK Calculator
Cash ISA Calculator 2026/27
Project tax-free interest on a UK Cash ISA and see how it compares to a regular taxable savings account. Compounded monthly. Based on 2026/27 HMRC allowances.
Your Cash ISA inputs
Your tax band (for comparison)Personal Savings Allowance: basic £1,000 · higher £500 · additional £0.
Projected Cash ISA balance after 5 years
£19,688
Tax-free
Total contributed
£17,000
opening balance + monthly deposits
Tax-free interest earned
£2,688
compounded monthly at 4.5% AER
Cash ISA vs taxable savings account (basic rate)
Cash ISA (tax-free)
£19,688
Interest: £2,688
Taxable savings
£19,688
After tax interest: £2,688
Illustrative tax saved with the ISA wrapper+£0
Educational information only — not regulated financial advice. Figures are illustrative, compounded monthly, and assume the AER rate stays constant for the whole term. Actual Cash ISA rates change, and provider terms vary. Always check current rates and your own tax position, or consult a regulated adviser.
Common Cash ISA questions
How much can I put in a Cash ISA in 2026/27?
The total annual ISA allowance is £20,000 across all ISA types. You can put all of it into a Cash ISA if you want, or split it across Stocks & Shares, Innovative Finance and Lifetime ISAs.
Is Cash ISA interest really tax-free?
Yes — interest inside a Cash ISA is free of UK income tax. Outside an ISA, interest is only tax-free up to your Personal Savings Allowance (£1,000 basic-rate, £500 higher-rate, £0 additional-rate).
Can I open more than one Cash ISA in a year?
Since April 2024, yes — you can pay into multiple Cash ISAs in the same tax year, provided your total contributions stay within the £20,000 allowance.
What rate should I use in this calculator?
Use the AER (Annual Equivalent Rate) advertised by your provider. Easy-access rates change frequently; fixed-rate ISAs lock the rate for a set term.