# Investment calculator UK: ISA growth after fees | ComputeNow

URL: https://computenow.co.uk/investment-calculator/

> See how regular investing could grow over time after fees, with a starting lump sum, in today’s money and against the ISA allowance.

This calculator shows a worked example below. To use your own figures, add them to the URL as query parameters (listed in https://computenow.co.uk/llms.txt), for example https://computenow.co.uk/investment-calculator/?<parameter>=<value>.

[What's Left, step 5 of 7: How much should I put aside?](https://computenow.co.uk/money-plan/#steps)

# Investment and ISA calculator

See how regular investing could grow over time, after fees.
Rates checked 18 October 2026
By the ComputeNow team, checked against GOV.UK and HMRC[Sources (2)](#sources)[How we calculate](https://computenow.co.uk/methodology/)

After 20 years you could have
£78,530.72
from £48,000 paid in, assuming 4.7% growth after fees. In today's money that is about £52,848.92.

Your £78,530.72

- Your payments £48,000.00 (61%)
- Growth £30,530.72 (39%)

## Where it comes from

| Item | Total |
| --- | --- |
| Your payments | £48,000.00 |
| Investment growth | £30,530.72 |
| Final value | £78,530.72 |

Outside an ISA or pension, dividends, interest and gains above your allowances are taxed; this illustration assumes an ISA.
This is an illustration, not advice or a forecast. Investments can fall as well as rise and you may get back less than you put in.

### Next steps

- [Pension calculator](https://computenow.co.uk/pension-calculator/)Compare with paying into a pension, which gets tax relief.

Added. [See what's left each month](https://computenow.co.uk/money-plan/)
[What's Left](https://computenow.co.uk/money-plan/) adds up your monthly figures from each calculator and shows what is left each month.
[After 20 years you could have £78,530.72 Breakdown](#result)

## Year by year

| Year | Paid in | Growth that year | Balance |
| --- | --- | --- | --- |
| Year 5 | £12,000.00 | £545.63 | £13,463.89 |
| Year 10 | £24,000.00 | £1,306.05 | £30,403.51 |
| Year 15 | £36,000.00 | £2,262.78 | £51,716.16 |
| Year 20 | £48,000.00 | £3,466.49 | £78,530.72 |

Showing every fifth year.

## How investment growth is estimated

We assume your money grows by the same rate every year, minus fees. Real returns go up and down.
In a stocks and shares ISA, growth and income are free of tax.

## Related calculators

[Pension calculator Your pension pot at retirement](https://computenow.co.uk/pension-calculator/)[Compound interest calculator How interest builds on interest](https://computenow.co.uk/compound-interest-calculator/)[Inflation calculator What money will be worth later](https://computenow.co.uk/inflation-calculator/)

## Guides and help

### Our guides

[How big could your pension be? Pension pots by the age you start saving](https://computenow.co.uk/guides/pension-pots-by-age/)

### Official services and free advice

[Individual Savings Accounts (ISAs) GOV.UK: tax-free saving and investing](https://www.gov.uk/individual-savings-accounts)[Tax on dividends GOV.UK: the dividend allowance and rates](https://www.gov.uk/tax-on-dividends)[Check your money is protected FSCS: cover if a bank or provider fails](https://www.fscs.org.uk/)[Check a firm is authorised FCA register: lenders, brokers and advisers](https://register.fca.org.uk/)

## Sources

Each source was last checked on 18 October 2026.

- [FCA: standard projection rates (COBS 13 Annex 2)](https://www.handbook.fca.org.uk/handbook/COBS/13/Annex2.html)
- [GOV.UK: Individual Savings Accounts](https://www.gov.uk/individual-savings-accounts)
These results are an estimate, not financial advice. They use the 2026/27 rates in force on 24 October 2026 and the inputs shown, so your actual tax, pay or costs may differ. Before making a decision about your money, check the figures with HMRC or your provider, or speak to a regulated financial adviser. Free, impartial guidance is available from MoneyHelper.
This page explains the rules using the 2026/27 rates in force on 24 October 2026. It is general information, not financial advice. For decisions about your own money, speak to a regulated financial adviser, or get free, impartial guidance from MoneyHelper.