ISA Calculator
Project how your Cash ISA and/or Stocks & Shares ISA could grow tax-free, with the £20,000 annual allowance and the upcoming £12,000 Cash ISA cap applied automatically.
Stocks & Shares ISA returns are not guaranteed and can go down as well as up. The figure above is an illustrative long-run assumption you can adjust.
Optional. This comparison is a simplified illustration only. Actual tax on savings interest and investment returns depends on your income, allowances, dividends, capital gains, tax rates and personal circumstances. The taxable comparison assumes the same intended annual contribution is made to a non-ISA account, even where part of that contribution cannot be sheltered in an ISA because of the Cash ISA limit.
ISA Balance Over Time
Year-by-Year Breakdown
Illustrative Comparison: ISA vs Taxable Account
This comparison is a simplified illustration only. Actual tax on savings interest and investment returns depends on your income, allowances, dividends, capital gains, tax rates and personal circumstances. The taxable comparison assumes the same intended annual contribution is made to a non-ISA account, even where part of that contribution cannot be sheltered in an ISA because of the Cash ISA limit.
ISA Calculator UK 2026
Our ISA Calculator helps you project how your Cash ISA and Stocks & Shares ISA savings could grow tax-free over time. It automatically applies the current £20,000 annual ISA allowance, and switches to the £12,000 Cash ISA cap from the 2027/28 tax year onwards — this reflects the government policy announced for the rules taking effect from 6 April 2027.
What Is the ISA Allowance for 2026/27?
For the current 2026/27 tax year, every UK adult has a £20,000 ISA allowance. This can be paid entirely into a Cash ISA, entirely into a Stocks & Shares ISA, or split between ISA types in any combination you choose, up to the £20,000 total.
What Is Changing to Cash ISAs From April 2027?
At Autumn Budget 2025, the government confirmed that from 6 April 2027, the amount savers under 65 can pay into a Cash ISA each tax year will fall from £20,000 to £12,000. The remaining £8,000 can be used in a Stocks & Shares ISA or another eligible ISA type, subject to that ISA’s own rules and limits, if you want to use more of the £20,000 overall allowance.
| Tax Year | Overall ISA Allowance | Cash ISA Cap (Under 65) | Cash ISA Cap (65+) |
|---|---|---|---|
| 2026/27 | £20,000 | £20,000 | £20,000 |
| 2027/28 onwards | £20,000 | £12,000 | £20,000 |
Savers aged 65 and over keep the full £20,000 Cash ISA allowance, starting from the tax year in which they turn 65. Money already held in a Cash ISA before 6 April 2027 is not affected and continues to grow tax-free under the new rules.
How to Use This Calculator
- Choose your ISA type – Cash ISA only, Stocks & Shares ISA only, or a split between the two.
- Set your split – if splitting, choose what percentage goes into cash versus stocks and shares.
- Enter your date of birth – the calculator works out the exact tax year your 65th birthday falls in, and applies the full £20,000 Cash ISA cap from the start of that tax year onwards.
- Enter your current ISA balance and planned annual contribution.
- Enter expected growth rates – a Cash ISA interest rate (AER) and/or a Stocks & Shares ISA expected annual return.
- Choose a projection period from 5 to 25 years.
- Optionally, tick the box to see an illustrative comparison against a taxable (non-ISA) account.
- Click Calculate ISA Growth to see your results.
Cash ISA vs Stocks & Shares ISA
| Feature | Cash ISA | Stocks & Shares ISA |
|---|---|---|
| Risk | Low – capital is generally protected | Higher – value can fall as well as rise |
| Typical returns | Tracks the Bank of England base rate and savings market | Potential for higher long-term returns, but values can fall and returns are not guaranteed. |
| 2026/27 annual limit | £20,000 | £20,000 |
| 2027/28 annual limit (under 65) | £12,000 | £20,000 (combined with Cash ISA up to £20,000 total) |
| Best suited to | Short-term savings, emergency funds | Long-term goals (5+ years) |
Why Is the Cash ISA Limit Being Reduced?
The government’s stated aim is to encourage more people to consider stocks and shares investing rather than holding all of their tax-free savings allowance in cash, on the basis that long-term investment returns have historically outpaced cash savings. The change was announced at Autumn Budget 2025 and confirmed on GOV.UK, with the £12,000 Cash ISA cap and related anti-circumvention rules taking effect from 6 April 2027.
Frequently Asked Questions
What is the ISA allowance for the 2026/27 tax year?
For the 2026/27 tax year, the total ISA allowance is £20,000, and the whole amount can currently be placed in a Cash ISA, a Stocks & Shares ISA, or split between them.
What is changing to Cash ISAs from 6 April 2027?
From 6 April 2027, the amount you can pay into a Cash ISA each tax year falls to £12,000 for savers under 65. The remaining £8,000 can be used in a Stocks & Shares ISA or another eligible ISA type, subject to that ISA’s own rules and limits, if you want to use more of the £20,000 overall allowance.
Does the overall £20,000 ISA allowance change in 2027?
No. The overall ISA allowance stays at £20,000. Only the amount that can go into cash is being reduced for savers under 65.
Are savers aged 65 and over affected by the Cash ISA change?
Savers aged 65 and over keep the full £20,000 Cash ISA allowance, starting from the tax year in which they turn 65. The government has said this exemption will apply “at least initially”.
What happens to money already in my Cash ISA?
The reduced £12,000 limit only applies to new contributions made from 6 April 2027 onwards. Money already held in a Cash ISA from previous tax years is not affected and continues to grow tax-free.
Is growth inside an ISA really tax-free?
Yes. Interest, dividends and capital gains earned inside a Cash ISA or Stocks & Shares ISA are free from UK income tax and Capital Gains Tax, regardless of how much you hold.
How does this calculator handle the 2027 Cash ISA change?
The calculator applies the £20,000 Cash ISA limit for the 2026/27 tax year, then applies a £12,000 limit from 2027/28 onwards. Using your date of birth, it identifies the exact tax year in which you turn 65 and applies the full £20,000 cap from the start of that tax year onwards, in line with GOV.UK rules – even if your birthday falls later in that tax year. For this projection, any amount above the Cash ISA cap is modelled as being allocated to your Stocks & Shares ISA when you have selected a split.
Is the taxable account comparison financial advice?
No. This comparison is a simplified illustration only. Actual tax on savings interest and investment returns depends on your income, allowances, dividends, capital gains, tax rates and personal circumstances. The taxable comparison assumes the same intended annual contribution is made to a non-ISA account, even where part of that contribution cannot be sheltered in an ISA because of the Cash ISA limit. It is not personalised financial or tax advice, and you should speak to a qualified adviser before making decisions.