ISA Calculator United Kingdom

What the ISA calculator does

The calculator projects how an Individual Savings Account could grow. Starting from your current balance and planned annual contributions, it applies an expected rate of return and shows the future value. For a Lifetime ISA it adds the government bonus on eligible contributions. Use it to see what steady tax-free saving could build for a first home, retirement or long-term growth.

What an ISA is

An ISA is a UK tax wrapper. Interest, dividends and capital gains inside it are free of UK tax, which is the main reason ISAs are so widely used for saving and investing.

A cash ISA works much like a savings account, offering stability, which suits short-term goals or money you cannot afford to lose. A stocks and shares ISA rises and falls with investment markets but has historically offered more growth over long periods. You set the expected return, so you can model either by choosing a rate that suits the account type.

The Lifetime ISA bonus

The Lifetime ISA is designed for buying a first home or saving for later life. You can open one between 18 and 39 and pay in up to £4,000 a year, and the government adds a 25% bonus, up to £1,000 a year.

Select Lifetime ISA and the projection includes the bonus, which can make a large difference over many years. The money can be withdrawn without penalty only to buy a first home (up to £450,000), from age 60, or if you are terminally ill. Other withdrawals bring a 25% charge, which takes back more than the bonus added, so check the rules before relying on one for a particular goal.

How the calculation works

• It starts with your current balance.
• It adds your annual contribution each year, capped at the allowance for the account type.
• For a Lifetime ISA, it adds the 25% bonus on eligible contributions.
• It compounds the balance at your expected rate of return.

The advanced options let you net off a platform fee, increase your contribution each year and show the result in today’s money after inflation. The output is the projected value at the end of your chosen period, split into contributions, bonus and growth.

For example, £5,000 already saved plus £4,000 a year at 7% grows to about £65,100 after ten years, of which £45,000 is money you paid in.

Why compounding matters

Inside an ISA, returns are reinvested and earn further returns without being taxed, so more of the growth keeps working for you. The earlier and more consistently you pay in, the more time your money has to compound, and small regular contributions kept up for many years can build a substantial balance.

What you need to enter

• Your current ISA balance.
• Your planned annual contribution.
• Your expected rate of return.
• The number of years to project.
• The account type, so the Lifetime ISA bonus is included where relevant.

For a stocks and shares ISA, use a cautious long-term return, since markets do not rise in a straight line. For a cash ISA, use a lower rate close to typical savings rates; applying investment-style growth to cash makes the projection misleading.

Reading your result

The result shows the projected value of your ISA, with any Lifetime ISA bonus already included. Comparing different contribution levels or returns shows how much the outcome depends on the choices you control.

Two people paying in the same amount can end up in very different places depending on when they start and how consistently they contribute. Keeping up contributions through market falls, rather than stopping, usually serves long-term savers best.

When to use this tool

• To project the growth of a cash or stocks and shares ISA.
• To see the effect of the Lifetime ISA bonus.
• To compare contribution levels towards a savings goal.
• To plan tax-free saving over the long term.

Revisit the projection as your balance grows or your contributions change.

This is general information only and not financial advice.

About This ISA Calculator

Use this ISA calculator to get an instant, accurate estimate. The figures follow official GOV.UK guidance and every rate and threshold is kept up to date for 2026. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.