ISA Calculator & Investment Planner (UK)
Plan your ISA contributions, returns, and allowance usage - free, simple, UK focused.
No sign up. UK tax rules. Updated annually. Results are estimates only.
Start with a free calculator
An ISA (Individual Savings Account) lets you save or invest up to £20,000 each tax year without paying UK income tax or capital gains tax on the interest or returns. Use these free calculators to estimate how a Cash ISA, Stocks and Shares ISA or Lifetime ISA could grow, and how much of your 2026-27 allowance is left. ISA rules correct as of 26 September 2026.
ISA Calculator
Plan contributions, growth and allowance usage. Estimates, not a forecast.
Cash ISA Calculator
Estimate how savings could grow at an interest rate you choose. Not a forecast.
Stocks & Shares ISA Calculator
Estimate long-term investing outcomes at a growth rate you choose, with optional charges. Not a forecast. Investments can go down as well as up.
Lifetime ISA Calculator
Estimate how a Lifetime ISA and its government bonus could add up for a first home or retirement. Not a forecast. Investments can go down as well as up.
More tools: Junior ISA Calculator, ISA vs Savings Calculator, Fixed-Rate ISA Switch Calculator, ISA Income Calculator, ISA Allowance Checker, Contribution Split Planner.
Advanced ISA Planner
Compare ISA scenarios side by side
£14.99 one-off, no subscription
When a single calculator is not enough, the Advanced ISA Planner lets you set up longer-term scenarios, combine different ISA types, including cash ISAs, and model multiple tax years in one place.
- Combine Cash and Stocks & Shares ISAs
- Model multiple tax years and allowances
- Adjust returns, contributions, and time horizons
- Compare scenarios side by side
A paid tool: a one-off purchase of £14.99, with no subscription. The free calculators are separate from the planner. See the refund policy. Figures are illustrations, not forecasts.
Learn about ISAs by topic
Plain-English guides, grouped by what you want to find out. For information only, not financial advice.
Allowances and rules
How much you can put in, how the tax year works and what the main ISA rules say.
Cash ISAs
How cash ISA interest works, what affects rates and how a cash ISA differs from other savings.
Stocks and Shares ISAs
How investing inside an ISA works, what shapes returns, and charges and risk.
Lifetime ISA
Eligibility, the government bonus, the withdrawal charge and using a Lifetime ISA for a first home.
Junior ISAs
Who can open and pay into a Junior ISA, the yearly limit and what changes at 16 and 18.
Transfers and withdrawals
Moving an ISA between providers, taking money out, flexible ISAs, moving abroad and what happens on death.
Tax and interest
Whether ISA interest is taxable, how the savings allowances work and whether an ISA goes on a tax return.
Planning and growth
Using calculators well, how compound growth works and planning for retirement with ISAs.
ISA rules at a glance · ISA glossary · All guides, newest first
How it works
1. Enter your details
Add your monthly or lump-sum contributions, an assumed return, and how much of your ISA allowance you plan to use. No personal details required.
2. See your estimate
View how your ISA could grow over time, including estimated returns and remaining allowance, using UK tax-year assumptions.
3. Try other options
Change contributions, time horizon or returns to compare scenarios and see how the figures change.
Frequently Asked Questions
An ISA (Individual Savings Account) is a UK tax-efficient way for you to save or invest. Any interest, dividends, or growth within an ISA is free from UK income tax and capital gains tax, up to your annual allowance.
Yes. You can use the core ISA calculators for free, with no sign-up required. Optional advanced planning tools may have a one-off fee.
The results are estimates based on the information you enter and standard UK tax-year assumptions. They’re designed to help you explore scenarios, not to provide personalised financial advice.
Yes. You can hold more than one ISA. You still need to follow the current rules for ISA types and total contributions each tax year.
No. ISAPLAN provides educational tools and calculators to help you understand how ISAs work. If you’re unsure about your situation, you may wish to speak to a regulated financial adviser.
The free calculators are ideal for quick calculations and simple scenarios. The Advanced ISA Planner is designed for users who want to explore multiple tax years, combine different ISA types, or compare scenarios in more detail.
Every figure on the free calculators comes from our ISA rules page, which shows each rule with its gov.uk source and the date it was last checked. For more, see all the FAQs, about ISAPlan, the ISA glossary, or contact us.