How much will my stocks and shares ISA be worth?
Enter what is already in the ISA, what you plan to add, the growth you want to assume and the yearly charges you pay. The calculator takes the charges off the growth, adds each payment, and compounds the result for the number of years you choose.
On the defaults, £10,000 already invested plus £500 a month, with an assumed 5% a year less 0.5% of charges, grows to £216,197 after 20 years. You put in £130,000 and growth adds £86,197. Without the charges the same plan would reach £229,435, so 0.5% a year costs £13,238 over the two decades. The payments use £6,000 of the £20,000 allowance each tax year, or 30%.
GOV.UK describes ISAs as a way to save tax-free, so the calculator takes no tax off the growth. The growth rate is an assumption, not a forecast: share prices fall as well as rise, and few years look like the average.
What is the ISA allowance for 2026/27?
GOV.UK states that in the 2026 to 2027 tax year the most you can save in ISAs is £20,000. You can put it all in one ISA or split it across several, and the tax year runs from 6 April to 5 April. HM Revenue and Customs said in its tax-free savings newsletter of November 2025, updated on 22 December 2025, that the £20,000 limit will stay the same until April 2031.
| Limit | 2026/27 | Notes |
|---|---|---|
| All your ISAs together | £20,000 | Shared by stocks and shares, cash, Lifetime and Innovative Finance ISAs |
| Lifetime ISA | £4,000 | Counts toward the £20,000; first payment before age 40, payments until 50 |
| Junior ISA | £9,000 | A child's own account |
| Cash ISA, including from 6 April 2027 | £20,000 | Within the £20,000 overall limit; a planned cut to £12,000 will not take effect |
To open an ISA you need to be 18 or over and resident in the UK, with limited exceptions for Crown servants and armed forces members abroad. The calculator reads the £20,000 figure from its dated rules, so it is updated in one place if the allowance changes.
What changes for ISAs from April 2027?
Less than was planned. An HM Revenue and Customs policy paper, Cash Individual Savings Account (ISA) limit reduction, published on 17 September 2026, set out a cut in the cash ISA limit to £12,000 a year for savers under 65 from 6 April 2027, inside the £20,000 overall limit, with rules to stop the cut being sidestepped, such as limits on transfers from stocks and shares ISAs into cash ISAs.
That cut has been dropped. HM Revenue and Customs said in its tax-free savings newsletter of 29 October 2026 that, as announced at the Autumn Budget 2026, the £20,000 cash ISA limit will be kept from 6 April 2027. The reduction and the anti-circumvention rules that came with it will not take effect, and the regulations that brought them in are to be revoked.
For a stocks and shares ISA the yearly room stays at £20,000, shared with any cash, Lifetime or Innovative Finance ISAs you pay into in the same tax year. The calculator assumes the money is invested, not held as cash.
What happens if I pay in more than the ISA allowance?
The allowance is a cap on what goes into ISAs each tax year, so the calculator never projects money above it. If your planned payments, plus anything you enter under Other ISAs this tax year, add up to more than £20,000, it uses only the room that is left and says how much would have to be invested outside an ISA. For example, £2,000 a month is £24,000 a year; the calculator uses £20,000, or £1,666.67 a month, and flags the other £4,000.
Withdrawals work differently from what many people expect. GOV.UK explains that with a flexible ISA you can take cash out and put it back in the same tax year. With an ISA that is not flexible, money taken out does not free up allowance: in GOV.UK's example, someone who pays in £10,000 and then withdraws £3,000 can still pay in only £10,000 more that year, not £13,000. Your provider can tell you which kind you hold. The calculator does not model withdrawals.
Monthly payments or one payment at the start of the tax year?
Choose Once a year and the calculator puts the whole year's payment in on the first day of each tax year, then applies a full year of growth. Monthly payments go in at the end of each month and grow at a monthly rate that compounds to exactly the yearly figure after charges.
Paying earlier gives the money longer to grow. Using the full £20,000 for 20 years from nothing at an assumed 4.5% after charges, one payment at the start of each tax year reaches £655,663. Spreading the same £20,000 as £1,666.67 a month reaches £640,266, about £15,396 less. Monthly payments also buy at different prices through the year, which this arithmetic does not capture.
How growth, charges and time change the result
Holding the default £10,000 start and £500 a month over 20 years, with 0.5% of charges:
- Assumed growth. At 3% a year the ISA reaches £171,402, at 5% £216,197 and at 7% £275,049.
- Time. After 5 years it is £45,958, after 10 years £90,768, after 20 years £216,197 and after 30 years £410,985. The payments in those cases total £40,000, £70,000, £130,000 and £190,000.
Charges matter more than their size suggests, because they come off every year of compounding. With 5% assumed growth on the default plan:
| Yearly charges | Value after 20 years | Cost against no charges |
|---|---|---|
| 0% | £229,435 | £0 |
| 0.25% | £222,703 | £6,732 |
| 0.5% | £216,197 | £13,238 |
| 1% | £203,832 | £25,603 |
| 1.5% | £192,281 | £37,154 |
Add a platform's percentage fee to the ongoing charge of each fund you hold to get the figure to enter. A fixed yearly fee in pounds can be turned into a percentage by dividing it by the ISA's value.
How to project an ISA in Excel
Excel's FV function gives the same answer for monthly payments once the yearly rate after charges is turned into a monthly one. In one cell put =(1+0.045)^(1/12)-1, which is 0.3675% a month. Then =FV(A1, 240, -500, -10000), with that cell as A1, returns 216,197.04 for the default plan. Payments and the starting value are negative because they are money you pay in.
For one payment at the start of each tax year use the yearly rate and a type of 1: =FV(0.045, 20, -20000, 0, 1) returns 655,662.74. To keep a spreadsheet inside the rules, cap the payment cell with MIN, for example =MIN(planned payment, 20000 - other ISA payments).
What this ISA calculator leaves out, and common mistakes
It applies one growth rate and one charge every year, so it cannot show a fall in markets, a change in charges, or withdrawals along the way. It assumes the £20,000 allowance holds for every year shown; HM Revenue and Customs has said it stays until April 2031, and the calculator keeps the same figure for any years after that. It does not cover Lifetime ISA bonuses, Junior ISAs, transfers between providers, or tax on investments held outside an ISA.
- Forgetting the other ISAs. A cash ISA or Lifetime ISA uses the same yearly allowance.
- Expecting a withdrawal to free up allowance. Only a flexible ISA lets you replace money taken out in the same tax year.
- Leaving out charges. A 1% yearly charge costs £25,603 on the default plan over 20 years.
- Mixing tax years. The allowance resets on 6 April, not 1 January.
- Treating the growth rate as a promise. It is the figure you choose to test, and results in real markets vary.
Glossary
ISA allowance: the most you can pay into all your ISAs in one tax year. Stocks and shares ISA: an ISA that holds investments such as shares and funds. Flexible ISA: an ISA that lets you replace money withdrawn in the same tax year. Ongoing charge: a fund's yearly cost as a percentage. Platform fee: what the provider charges to hold the ISA. Tax year: in the UK, 6 April to the following 5 April.
Frequently asked questions
What is the ISA allowance for 2026/27?
£20,000 across all your ISAs, according to GOV.UK. A Lifetime ISA can take up to £4,000 of it. HM Revenue and Customs has said the £20,000 limit stays the same until April 2031.
How much will £500 a month in a stocks and shares ISA be worth after 20 years?
Starting from £10,000 and assuming 5% growth a year less 0.5% of charges, about £216,197. You would have paid in £130,000. At an assumed 3% the figure is £171,402, and at 7% it is £275,049.
Is the cash ISA limit changing in 2027?
No. A cut to £12,000 a year for savers under 65 from 6 April 2027 was set out in an HM Revenue and Customs policy paper of 17 September 2026, but HM Revenue and Customs said on 29 October 2026 that, as announced at the Autumn Budget 2026, the £20,000 cash ISA limit will be kept and the cut will not take effect.
Can I put the full £20,000 into a stocks and shares ISA after April 2027?
Yes, on the rules HM Revenue and Customs has published. The overall £20,000 limit is unchanged and can go into one stocks and shares ISA or be split with other ISAs. The calculator uses £20,000 as the yearly room.
What happens if I pay more than £20,000 into ISAs?
The allowance is the most you can pay into ISAs in a tax year, so the calculator caps your payments at the room left and tells you how much would need to go outside an ISA.
Does withdrawing money give me back ISA allowance?
Only with a flexible ISA, which lets you put money back in the same tax year. With an ISA that is not flexible, a withdrawal does not restore the allowance you have used. Your provider can tell you which type you have.
Is it better to pay into an ISA monthly or as a lump sum?
In this calculator's arithmetic, money paid in earlier has longer to grow, so £20,000 at the start of each tax year for 20 years ends about £15,396 above the same amount paid monthly, at an assumed 4.5% after charges. Real results depend on prices over the year, which the calculator does not model.
How much do ISA charges cost over time?
On £10,000 plus £500 a month for 20 years at an assumed 5%, a 0.5% yearly charge costs £13,238 and a 1% charge costs £25,603, compared with no charges at all.
Do I pay tax on a stocks and shares ISA?
GOV.UK describes ISAs as a way to save tax-free, so the calculator shows no tax on the growth. Tax rules for investments held outside an ISA are different and are not part of this page.
Who can open a stocks and shares ISA?
GOV.UK says you must be 18 or over and resident in the UK, with limited exceptions for Crown servants, armed forces members and their spouses or civil partners living abroad.
Courses behind investing through an ISA
ETF Exchange Traded Funds Investing and Trading Course
Introduction to exchange-traded funds, covering how ETFs combine stock and mutual fund features and how to use them for portfolio construction.
See what the course coversStock Market Trading Beginners Course
Structured online beginner program covering UK, USA, and European stock markets, technical analysis, fundamental analysis, risk management, and trading psychology.
See what the course coversFundamental Analysis Online Crash Course
Introductory course on evaluating companies before investing, covering fundamental analysis, business performance, market value, and practical stock selection methods.
See what the course coversSources and review
Last reviewed 13 November 2026 by the NIFM Academy editorial team. Next review by 5 April 2027.
United Kingdom, tax year 2026/27. Next review by 5 April 2027.
- GOV.UK, Individual Savings Accounts (ISAs), in the 2026 to 2027 tax year the maximum you can save in ISAs is 20,000 pounds; you can save tax-free; you must be 18 or over and resident in the UK, or a Crown servant or armed forces member abroad or their spouse or civil partner. Checked 13 November 2026.
- GOV.UK, How ISAs work, up to 20,000 pounds every tax year in one account or split across several; the tax year runs from 6 April to 5 April; a Lifetime ISA takes up to 4,000 pounds a tax year. Checked 13 November 2026.
- GOV.UK, Withdrawing your money from an ISA, a flexible ISA lets you take cash out and put it back in the same tax year; with a non-flexible ISA a withdrawal does not restore the allowance. Checked 13 November 2026.
- GOV.UK, Lifetime ISA, up to 4,000 pounds a year until age 50; the first payment must be made before age 40. Checked 13 November 2026.
- GOV.UK, Junior Individual Savings Accounts, the Junior ISA savings limit is 9,000 pounds in the 2026 to 2027 tax year. Checked 13 November 2026.
- HM Revenue and Customs, Tax-free savings newsletter 19, November 2025, updated 22 December 2025, the ISA annual subscription limit remains 20,000 pounds until April 2031; Lifetime ISA 4,000 and Junior ISA 9,000 pounds unchanged until April 2031. Checked 13 November 2026.
- HM Revenue and Customs, Tax-free savings newsletter 24, 29 October 2026, as announced at the Autumn Budget 2026, the cash ISA limit stays at 20,000 pounds from 6 April 2027; the planned reduction to 12,000 pounds and the anti-circumvention rules that came with it will not take effect. Checked 13 November 2026.
- HM Revenue and Customs, Tax-free savings newsletter 24, published 29 October 2026, as announced at the Autumn Budget 2026, the annual cash ISA limit of 20,000 pounds will be retained from 6 April 2027; the reduction of the cash ISA limit and associated anti-circumvention rules will not take effect, and the regulations that introduced the 12,000 pound limit will be revoked. Checked 13 November 2026.