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ISA calculator

What could a Stocks & Shares or cash ISA be worth, and what does the tax wrapper actually save you? Two plain-English estimates - free, no sign-up, education only.

The projection

What could my ISA be worth?

Put in a starting amount, what you add each month, how long for, and a rate. For a cash ISA that rate is the interest you are paid; for a stocks and shares ISA it is a growth assumption you are choosing, not a rate anyone can promise you. The split below shows how much of the final figure is your own money and how much is growth on top.

Try a rate
Could grow to about-
You put in -Growth on top -

An illustration of how compounding works, not a forecast or advice. It assumes a steady yearly return, but real markets are bumpy and can fall as well as rise - some years will be negative. Past performance doesn't predict the future, and this doesn't account for fees, tax or inflation.

Everything here stays inside the wrapper, so nothing is deducted for UK tax on the way. The £20,000 yearly allowance is the one limit to keep in mind: that is the most you can pay in across all your ISAs in a tax year, so monthly contributions above roughly £1,666 would take you past it.

The tax saving

What does the ISA wrapper actually save?

The projection above is the same arithmetic whether the money is sheltered or not. This is the part that is specific to an ISA: what you would have handed over in dividend and capital gains tax if the same money had been held in an ordinary account instead.

The UK tax shelter

Would an ISA actually save you tax?

A Stocks & Shares ISA shelters your investments from UK tax on dividends and gains. Here's a rough idea of what that's worth on a lump sum, versus a normal (‘taxed’) account. Illustrative only - 2026/27 allowances, not advice.

Common questions

ISA calculator questions

How much can I put in an ISA each year?

£20,000 per tax year (6 April to 5 April), across all your ISAs added together rather than £20,000 each. A Lifetime ISA has its own £4,000 sub-limit inside that total, and a Junior ISA has a separate £9,000 allowance. Allowances can change between tax years, so gov.uk always has the current figures.

What growth rate should I put in the calculator?

There is no correct answer, which is the honest one. A long-run global shares average is often quoted somewhere around 5-7% a year before inflation, but real returns arrive in a jagged line rather than a steady rate - some years are strongly positive and some are sharply negative. The figure you type is an assumption, not a forecast, and the useful thing to do with it is try a low one and a high one and look at the gap between them.

What is the difference between a cash ISA and a stocks and shares ISA?

A cash ISA pays interest and the balance does not fall. A stocks and shares ISA holds investments, which can grow more over long periods and can also lose value. The tax shelter works the same way in both; what differs is what is inside and how it behaves. The projection above suits either - put an interest rate in for cash, a growth assumption in for investments.

Does the calculator account for inflation?

No. The figures are in today's pounds without adjusting for rising prices, so a pot 20 years out will not stretch as far as the same number suggests today. A rough way to see the difference is to run it once at your assumed rate and again at that rate minus around 2-3%, which is the sort of gap inflation has historically made.

Is any of this a prediction of what I will actually get?

No. It is arithmetic on the numbers you type. It assumes a steady rate that real markets do not deliver, ignores charges unless you subtract them from the rate yourself, and cannot know what happens next. Treat it as a way to understand how compounding and the ISA wrapper behave, not as a forecast of your own outcome.

The full rules - what you can hold, what an ISA does not shelter, and what happens when you take money out or move providers - are on the ISA rules page. For the same compounding maths outside a wrapper, see the investment growth calculator.

You've got the foundations. Now have a look around.

Explore the namesBrowse 600+ shares and funds - filter by dividends, cheap-and-quality or growth, and open any one for the plain-English version.Build a practice piePut a pretend portfolio together and watch how it would have moved - no account, no real money, no pressure.Look up a companyType a name you recognise - Apple, Lloyds, a Vanguard fund - and read what it actually is, with the jargon already decoded.Find your fitAnswer two quick questions - what you're drawn to and which market - and see a handful of names that match, with the plain-English reason why.How to research a shareA plain-English, 20-minute checklist: what a company does, how it makes money, and the honest risks - and where to find each.

Where these figures come from

The rules and allowances on this page come from the official sources below. Tax rules change, so check the source for the current position.