UK ISA Calculator 2026/27
Project your ISA balance for 2026/27 and beyond. Compare Cash ISA interest and Stocks and Shares ISA investment returns using the £20,000 annual allowance.
Last updated: May 2026
Historical S&S ISA average: 6–8%
Final ISA Value
£429,303
Total Contributions
£205,000
Tax-Free Growth
£224,303
Taxable Account Value
£367,291
ISA Tax Saving
£62,012
Annual Return Rate
7.0%
| Year | Total Contributed | ISA Balance | Tax-Free Growth |
|---|---|---|---|
| 1 | £15,000 | £15,350 | £350 |
| 2 | £25,000 | £26,425 | £1,425 |
| 3 | £35,000 | £38,274 | £3,274 |
| 4 | £45,000 | £50,953 | £5,953 |
| 5 | £55,000 | £64,520 | £9,520 |
| 6 | £65,000 | £79,037 | £14,037 |
| 7 | £75,000 | £94,569 | £19,569 |
| 8 | £85,000 | £111,189 | £26,189 |
| 9 | £95,000 | £128,972 | £33,972 |
| 10 | £105,000 | £148,000 | £43,000 |
| 11 | £115,000 | £168,360 | £53,360 |
| 12 | £125,000 | £190,145 | £65,145 |
| 13 | £135,000 | £213,456 | £78,456 |
| 14 | £145,000 | £238,398 | £93,398 |
| 15 | £155,000 | £265,085 | £110,085 |
| 16 | £165,000 | £293,641 | £128,641 |
| 17 | £175,000 | £324,196 | £149,196 |
| 18 | £185,000 | £356,890 | £171,890 |
| 19 | £195,000 | £391,872 | £196,872 |
| 20 | £205,000 | £429,303 | £224,303 |
Reviewed by Sneha Iyer, CFP
•Certified Financial PlannerSpecializing in wealth management and retirement planning. Sneha validates the investment projection models and compound interest algorithms used across our financial tools. All mathematical models and regulatory data points have been verified for the current 2026 fiscal period.
What is an ISA?
An Individual Savings Account (ISA) lets UK residents save or invest up to £20,000 per year completely free of income tax and capital gains tax. Interest, dividends, and capital gains within an ISA are never taxed.
The two main types are Cash ISA (fixed or variable interest rate, low risk) and Stocks and Shares ISA (invested in funds, shares, or bonds, higher long-term return potential but with risk). Unused allowance cannot be carried forward to the next year.
How to use this calculator
- 1Enter monthly contribution — Input how much you plan to add to your ISA each month.
- 2Set return rate — Choose the interest or investment return rate you expect.
- 3Set time period — Enter how many years you plan to save or invest.
- 4Add existing balance — Include any ISA savings you already have to see the total projection.
Formula & example
ISA Value = (Annual Contribution x ((1 + r)^n - 1) / r) + Existing Balance x (1 + r)^n
Example: Contributing 500 per month to a Stocks and Shares ISA at 7% annual return. After 20 years the ISA value is approximately 262,000, with 120,000 contributed and 142,000 growth.
Benefits
Tax-free growth
All growth inside an ISA is exempt from income tax and CGT.
2026/27 allowance
Uses the current £20,000 annual ISA allowance.
Long-term projection
Visualise how compound growth builds wealth over 10, 20, or 30 years.
Allowance awareness
The calculator flags when annual contributions exceed the annual limit.
Use cases
Saving for retirement
Build a tax-free income source to complement your workplace pension.
House deposit
Project ISA growth toward a first home deposit, including Lifetime ISA bonus.
Education fund
Save for a child's future university costs in a tax-free Junior ISA.
General wealth building
Grow investments without paying tax on dividends or capital gains.
Frequently asked questions
What is the ISA allowance for 2026/27?+
The ISA allowance for 2026/27 is £20,000. This can be split across multiple ISA types (Cash ISA, Stocks and Shares ISA, Innovative Finance ISA) in the same tax year.
Can I withdraw money from an ISA?+
Yes. Most ISAs allow flexible withdrawals. If you withdraw from a flexible ISA, you can replace the money in the same tax year without it counting as a new contribution. Check your ISA terms before withdrawing.
What is a Lifetime ISA?+
A Lifetime ISA (LISA) allows you to save up to £4,000 per year and receive a 25% government bonus (up to £1,000 per year). The money must be used to buy a first home or accessed at age 60.
Is a Cash ISA better than a savings account?+
A Cash ISA protects your interest from income tax. If your savings interest exceeds the Personal Savings Allowance, a Cash ISA is more tax-efficient.
What happens to my ISA if I die?+
Your ISA passes to your spouse or civil partner as an Additional Permitted Subscription (APS), allowing them to invest an extra amount equal to your ISA value. ISAs form part of your estate for inheritance tax purposes.