ISA Calculator: Savings Growth and Lifetime ISA Bonus

Use the calculator

Current ISA balance (£)

Amount paid in each year (£)

Assumed growth or interest rate (% a year)

Number of years

Lifetime ISA?

Your age now (Lifetime ISA only)

Your estimate appears here.

How this calculator works

An Individual Savings Account (ISA) lets you save or invest without paying tax on the interest, dividends or gains. You can pay in up to £20,000 each tax year, split across cash, stocks and shares, innovative finance and Lifetime ISAs as you like. This calculator projects how a balance could grow:

It adds your yearly payment at the start of each year, limited to £20,000 (or £4,000 for a Lifetime ISA).
For a Lifetime ISA it adds the government bonus of 25% of what you pay in, up to £1,000 a year. Payments stop from age 50, so enter your age.
It then applies your chosen rate once a year, so growth compounds.

The result shows the final balance, the total you paid in, the total bonus and the growth. The rate you choose is an assumption, not a forecast. Cash ISA rates change, and stocks and shares can fall as well as rise. Try a few rates to see a range of outcomes. The figures are not adjusted for inflation.

Worked examples

These figures come from running this calculator and were checked by hand.

Example 1: full ISA allowance

Paying in £20,000 a year for 10 years at 5% gives £264,135.74: £200,000 paid in and £64,135.74 of growth.

Example 2: Lifetime ISA from age 30

Paying £4,000 a year for 10 years at 4% earns a bonus of £1,000 a year. The projected balance is £62,431.76: £40,000 paid in, a £10,000 bonus and £12,431.76 of growth.

Example 3: building up slowly

Starting with £10,000 and adding £5,000 a year for 20 years at 3% gives £156,443.54, of which £46,443.54 is growth.

ISA allowances for 2026/27

Item	Amount or rule
Total ISA allowance	£20,000 a tax year
Lifetime ISA limit	£4,000 a year, counted within the £20,000
Lifetime ISA bonus	25% of payments, up to £1,000 a year
Lifetime ISA age to open	18 to 39
Lifetime ISA payments	Allowed until you reach 50

Assumptions and what this calculator does not cover

Timing: payments are added at the start of each year and growth is applied yearly. Monthly saving or monthly bonus payments will give slightly different results.
Charges: platform and fund fees are not deducted. Include them by lowering the rate.
Inflation: results are in future pounds and are not adjusted for rising prices.
Allowance changes: the calculator assumes the current allowances stay the same each year.
Withdrawals: it assumes you take nothing out.

Lifetime ISA rules to know

A Lifetime ISA is for buying your first home or for later life. You can use it towards a first home costing up to £450,000, or withdraw from age 60. If you take money out for any other reason, apart from terminal illness, you pay a 25% government withdrawal charge. That takes back the bonus and some of your own money as well. Before you choose a Lifetime ISA over a pension, compare the two: workplace pensions often come with employer contributions, which a Lifetime ISA does not have.

If you are saving for a deposit, the mortgage affordability calculator gives a rough idea of the price range your deposit and income could support. For general saving targets, see the savings goal calculator and the compound interest calculator.

Do you need an ISA for cash savings?

Many people already pay no tax on savings interest thanks to the Personal Savings Allowance: £1,000 for basic-rate taxpayers, £500 for higher-rate taxpayers and nothing for additional-rate taxpayers. An ISA becomes more useful as your savings grow, if you pay tax at a higher rate, or if you invest.

Choosing a rate to try

For a cash ISA, start with the rate your provider is offering now, and remember that variable rates can fall. For a stocks and shares ISA, there is no guaranteed return. Trying a low, a middle and a higher rate gives a more honest picture than a single figure. Once you have a target, the budget planner can help you find the monthly amount to pay in.

Frequently asked questions

How much can I put in an ISA in 2026/27?

Up to £20,000 in total across all your ISAs in the tax year.

How much is the Lifetime ISA bonus?

25% of what you pay in, up to £1,000 a year on the maximum £4,000.

Who can open a Lifetime ISA?

UK residents aged 18 to 39. You can keep paying in until you are 50.

Does a Lifetime ISA count towards the £20,000 allowance?

Yes. Up to £4,000 of your £20,000 can go into a Lifetime ISA.

Sources

Rates for tax year 2026/27, last reviewed October 2026.

Results are estimates for planning, not financial or tax advice. See our terms and methodology.