Cash ISA calculator
Invest , add a month for at , and your Cash ISA could be worth:
These projections are examples, not a guarantee of future returns.
We’ve designed this calculator to give an indication of how your savings could grow. The figures shown aren’t guaranteed, as actual returns will depend on interest rates, account terms, tax, and your personal circumstances. It doesn’t consider inflation or charges, and isn’t financial advice.
What is a Cash ISA?
A Cash ISA is a savings account where all the interest you earn is tax‑free.
You can save up to £20,000 each tax year. Depending on your provider, you could be paid interest monthly or annually. Because returns are sheltered from tax, every penny of interest you earn is yours to keep.
How our Cash ISA calculator works
Our Cash ISA calculator is personalised to your situation, helping you work out how much you could save with regular contributions over a specified period.
To work out your results, our calculator assumes the following:
- All cash, including any interest earned, stays invested for the entire timeframe.
- The interest rate stays the same for the whole timeframe.
- Your regular contributions stay the same amount for the entire timeframe.
The Flagstone Cash ISA
Most ‘flexible’ Cash ISAs aren’t flexible at all. Most have strings attached – restrictions on withdrawals, hidden penalties, conditions and caveats.
But the Flagstone Cash ISA offers true flexibility. Spread cash between multiple banks in a single ISA, withdraw and redeposit as many times as you need, and make the most of your allowance. No hassle. No limits.
Transfer your existing ISAs to Flagstone today, for free, and enjoy complete convenience.
Cash ISA FAQs
Are Cash ISAs worth it?
Cash ISAs are one of the few ways to earn interest completely free of tax. Maximising your £20,000 allowance each year adds an accessible, predictable element to a balanced portfolio – a stable counterpart to longer-term or higher-risk investments.
Can you have multiple Cash ISAs?
Yes. Since April 2024, you can open and contribute to multiple Cash ISAs in the same tax year – as long as your combined contributions stay within the £20,000 annual allowance.
Spreading savings across providers can help you access competitive rates and keep balances within the FSCS protection limit per banking group.
Can I put £20,000 in a Cash ISA every year?
Yes, the current annual Cash ISA allowance is £20,000. From April 2027, this reduces to £12,000 for those under 65. Those aged over 65 will keep the full £20,000 allowance.
One Cash ISA, multiple banks.
Consolidate your scattered Cash ISAs in one platform, spread savings between multiple banks, and move money to higher rates in moments.
It’s the Flagstone you know – now for Cash ISA.
