Planning and growth
Using calculators well, how compound growth works and planning for retirement with ISAs.
For information only, not financial advice.
Guides on planning with ISAs: how to use a calculator and read its results, how compound growth works, and how ISAs can fit alongside other retirement saving. All figures are illustrations at assumptions you choose, not forecasts.
Quick answers
Do the calculators forecast what an ISA will be worth?
No. They show illustrations from the figures and the rate you enter, not forecasts. Investment values can go down as well as up, and results are not guaranteed.
Where do the allowance and tax-year figures come from?
Every limit comes from the ISA rules page, which shows each rule with its gov.uk source and the date it was last checked (26 September 2026).
Rules data last checked against gov.uk on 26 September 2026. For information only, not financial advice.
Tools for this topic
ISA Calculator
Estimate how a lump sum and monthly savings could grow, and see how much of this tax year's allowance is left.
ISA Income Calculator
Test what could be left after regular withdrawals, at three returns you choose.
Stocks & Shares ISA Calculator
Estimate how investments could grow at an assumed return, with optional charges. Investments can go down as well as up.
Guides
- How to Use an ISA Calculator: Inputs, Scenarios and Limits
What an ISA calculator needs, how to compare scenarios across Cash, Stocks and Shares and Lifetime ISAs, and what results leave out. Information only.
- How Do ISA Calculators Work? Reading the Returns They Show
How an ISA calculator turns balance, contributions, rate and time into a projected return, how to read nominal and real figures, and what it leaves out.
- Compound Interest ISA Calculator UK: How Compounding Works
How compound interest works in an ISA, with a two-saver example, the effect of charges and a calculator's limits. An illustration, not a forecast.
- ISA Growth Projection Calculator: What a Projection Shows
What an ISA growth projection calculator needs and shows: inputs, three growth rates, charges and inflation, with a 20-year example. Not a forecast.
- What Affects ISA Returns? Type, Timing, Charges, Allowance
How ISA type, contribution timing, charges and the annual allowance can affect an ISA's returns, with a worked example. Information only, not advice.
- ISA Millionaire Calculator: What a £1 Million Figure Shows
An illustration of what a monthly amount and an assumed growth rate could add up to in an ISA. Not a forecast; values can fall as well as rise.
- ISA Planning for Retirement: How ISAs and Pensions Differ
How ISAs can be used for retirement saving, how the different ISA types and the Lifetime ISA work, and how ISAs differ from pensions. Not advice.
See also the ISA rules at a glance, the ISA glossary and all topics.