UK ISA Calculator 2024-25
Project your ISA growth and tax savings for 2024/25. Covers Stocks & Shares ISA, Cash ISA, and Lifetime ISA (LISA) with government bonus and annual allowance limits.
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How to use this calculator
- 1
Choose Stocks & Shares ISA, Cash ISA or Lifetime ISA (LISA). The choice changes the contribution cap the tool applies, whether a bonus is added and which summary lines are shown.
- 2
Enter a monthly contribution. If it is above the monthly equivalent of the annual limit built into the tool, the tool uses the capped figure and says so in a note.
- 3
Enter your current balance, an expected annual return as a steady percentage and the number of years to project.
- 4
Read the projected balance together with total contributed, growth and, for a LISA, the bonus total. Change the return to see how sensitive the result is.
Frequently asked questions
How does this tool project an ISA balance?
It converts the annual return into a monthly rate by dividing by 12, then compounds your current balance and a level monthly contribution over years × 12 months using the standard future-value formula for regular payments made at the end of each month. The return is a single steady rate, so there is no volatility, no sequence of good and bad years, and no platform or fund charges.
What annual limits does the tool apply, and for which tax year?
The page is labelled 2024-25. The figures built into this tool are £20,000 a year for Stocks & Shares and Cash ISAs and £4,000 a year for a LISA. Your monthly figure is capped at one twelfth of that limit (about £1,667 or £333), and a note appears when the cap bites. The tool does not track other ISAs you may have subscribed to in the same year.
How is the Lifetime ISA bonus handled?
When LISA is selected, this tool adds 25% of each monthly contribution to the pot as a bonus and compounds it along with your own money. The bonus total is shown as a separate line. Your existing balance is treated as already in the account and earns growth, but it does not generate a bonus. Withdrawal charges, age limits and property-price limits are not modelled.
Why do Stocks & Shares and Cash give the same result?
Because the only difference the tool makes between them is the label. Both use the same £20,000 cap and the same compounding formula, so identical inputs give identical balances. The difference between the two products in practice is the return you enter, which is why the return field is yours to set rather than fixed per product.
What is the “estimated tax saving” line?
For Stocks & Shares and Cash it is simply 20% of the projected growth, shown as what a basic-rate taxpayer might otherwise owe on that growth. It ignores the personal savings allowance, the dividend allowance, the capital gains exemption and any higher-rate liability, so it is a rough indicator, not a tax calculation. It is not shown for a LISA.
What happens with zero or blank values?
A return of 0% is respected and gives a straight-line result of balance plus contributions. A cleared return box counts as 0%, which is the straight-line case above. A period of 0, which is also what a cleared period box becomes, returns your current balance unchanged, and negative contributions or balances are treated as zero.
Do these figures stay current?
No automatic updating takes place. ISA limits, the LISA bonus rate and related rules change at least every tax year, and the tables in this tool are not refreshed to match. HMRC’s published rules, or a qualified adviser, govern what applies to your own circumstances.
UK ISA growth projections: compounding monthly contributions and the LISA bonus
How the projection is built
The calculation turns your annual return into a monthly rate, adds one contribution at the end of every month and compounds the lot for the number of years you enter. Your starting balance is compounded on its own over the same period. The monthly contribution is limited to one twelfth of the annual limit built into the tool, labelled 2024-25: £20,000 for Stocks & Shares and Cash, £4,000 for a Lifetime ISA. When a LISA is chosen, 25% of every contribution is added to the pot and grows with it. Charges, inflation and market swings are not modelled, because the return is one fixed percentage.
Three worked examples
A Stocks & Shares ISA with £500 a month, no starting balance, 5% a year and 10 years projects to £77,641, made up of £60,000 contributed and £17,641 of growth; the tool’s 20% indicator puts the notional tax on that growth at £3,528. Entering £2,000 a month into a Cash ISA with £10,000 already saved, 0% return and 5 years triggers the cap: the tool uses £1,667 a month, so £100,000 is contributed and the balance is £110,000 with no growth. A LISA at £250 a month with £5,000 saved, 4% and 20 years reaches £125,730, of which £60,000 is your contributions, £15,000 is bonus and £45,730 is growth.
One set of inputs, three ISA types
The table feeds the same inputs through each ISA option: £300 a month, a £2,000 starting balance, 4% a year and 15 years. It shows that the first two options behave identically, because only the return you type in distinguishes them, while the LISA option adds £13,500 of bonus and compounds it for a markedly larger pot.
| ISA type selected | Projected balance | Contributed | Bonus | Growth | Tax-saving line |
|---|---|---|---|---|---|
| Stocks & Shares | £77,468 | £54,000 | None | £21,468 | £4,294 |
| Cash | £77,468 | £54,000 | None | £21,468 | £4,294 |
| Lifetime ISA | £95,925 | £54,000 | £13,500 | £26,425 | Not shown |
What the figure leaves out
Fund charges, platform fees, inflation and the timing of returns all affect a real ISA and none appear here. Contributions are assumed level through the year and returns steady, whereas actual markets move unevenly and a cash rate can change. The tax-saving line is a single flat 20% of growth, so it ignores the allowances that decide how much tax would really arise outside an ISA. Withdrawals, transfers and subscriptions to other ISAs are not tracked.
Where the built-in limits come from
The £20,000 and £4,000 limits and the 25% bonus rate are the figures built into this tool, labelled 2024-25, and they are not presented here as current law. These rules change at least every tax year and the tool’s tables are not updated automatically, so HMRC, or a qualified adviser, governs what applies to you. Use the projection to compare scenarios, such as a different return or period, rather than to forecast an exact outcome.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →