UK Investment Calculator — Pound Cost Averaging
Project what a starting amount plus monthly investing could build in pounds—inside a Stocks & Shares ISA or GIA, with fees and inflation.
Published by GrowThenDraw Editorial Team · Editorial policy · Methodology & sources
If you sold everything at the end (one tax year, taxable account): estimated tax £4,709 — you keep £82,338.
| Year | Invested | Value | Gain |
|---|---|---|---|
| 1 | £6,000 | £6,232 | £232 |
| 2 | £12,000 | £12,915 | £915 |
| 3 | £18,000 | £20,082 | £2,082 |
| 4 | £24,000 | £27,766 | £3,766 |
| 5 | £30,000 | £36,005 | £6,005 |
| 6 | £36,000 | £44,841 | £8,841 |
| 7 | £42,000 | £54,314 | £12,314 |
| 8 | £48,000 | £64,473 | £16,473 |
| 9 | £54,000 | £75,367 | £21,367 |
| 10 | £60,000 | £87,047 | £27,047 |
Pound cost averaging, SIP and regular investing
Invest the same number of pounds each month and a lower market price buys more units while a higher price buys fewer. The FCA describes this as a way regular monthly purchases can smooth the effect of short-term market moves. It does not guarantee a profit or protect the final balance from a falling market.
In Britain this is usually called regular investing or pound cost averaging. Indian investors know the same contribution pattern as a systematic investment plan, or SIP. Do not confuse that with a UK Share Incentive Plan or a SIPP pension: similar letters, different products.
A £500-a-month worked example
At the editable 7% annual return assumption, with no fees and each contribution added at the start of the month, £500 monthly for 10 years projects to about £87,047. You contribute £60,000 and the smooth model attributes about £27,047 to growth.
That is a worked scenario, not a forecast. Try lower and higher returns, add the fund and platform costs you actually expect, and keep the inflation view switched on. A plan that works only at the highest return assumption is not yet a robust plan.
ISA, GIA, fees and tax
The 2026/27 ISA subscription allowance is £20,000 across your ISAs. Income and capital gains inside a Stocks & Shares ISA are tax-free. A GIA has no ISA wrapper: dividend tax can arise while you hold investments and CGT can arise when you sell. The calculator's GIA result estimates CGT on a sale at the end; it does not model dividend tax during the growth phase.
Fund OCFs, platform fees and dealing charges reduce what compounds. Enter recurring percentage costs in the expense-ratio field; reduce the monthly contribution if a fixed dealing charge comes out of every payment. The return remains an editable assumption, not a promise from the FTSE or any provider.
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Frequently asked questions
What is a pound cost averaging calculator?
It projects the result of investing a fixed amount in pounds at regular intervals. Each contribution compounds for a different length of time, so the calculator runs the plan month by month and separates total contributions from projected growth.
How much could £500 a month grow to in 10 years?
At a smooth 7% annual return with no fees and contributions at the start of each month, £500 monthly projects to about £87,047 after 10 years. £60,000 is contributed and about £27,047 is projected growth. Actual returns will be uneven and may be lower or negative.
Is pound cost averaging the same as a SIP in the UK?
The monthly-investing calculation is the same as an Indian systematic investment plan. In UK law, however, SIP commonly means Share Incentive Plan and SIPP means a personal pension, so this calculator uses the local phrase pound cost averaging to avoid confusing the products.
Does pound cost averaging guarantee a profit?
No. Regular purchases spread entry dates, but the investments can still fall and you can get back less than you put in. Return assumptions are only scenarios; investment choice, market performance, fees and the time you sell determine the actual result.
How much can I put into a Stocks & Shares ISA in 2026/27?
The total ISA subscription allowance is £20,000 for the 2026/27 tax year across your ISAs. That averages £1,666.67 a month if spread evenly, but the legal limit is annual and includes subscriptions to other ISA types.
Tax figures for 2026/27 last verified 26 July 2026 against the official source — how we calculate.
GrowThenDraw is not authorised or regulated by the Financial Conduct Authority and does not provide financial advice. All results are educational estimates only — consider advice from an FCA-authorised financial adviser before acting.
Relevant bodies in this jurisdiction: FCA (financial conduct), HMRC (tax).