See what your investing could be worth. Choose a monthly amount (a SIP — Systematic Investment Plan) or a one-off lump sum, set an expected annual return and a period, and get the future value with the growth broken down year by year.
⚖︎ Results are for informational purposes and do not constitute tax advice. For specific situations, consult a licensed accountant or the relevant tax authority.
iHow it is calculated
The calculator compounds your money monthly at the expected annual return. In SIP mode each monthly contribution is invested and then grows for the rest of the term (an annuity-due); in lump-sum mode a single amount compounds for the whole period. The future value of a level monthly SIP is:
FV = P × ((1 + i)^n − 1) / i × (1 + i)
Investing £1,000 a month for 15 years at an assumed 8% return grows to ≈ £348,000. You put in £180,000, so about £168,000 is investment growth — more than your own contributions.
?Frequently asked questions
What is a SIP (Systematic Investment Plan)?
A SIP means investing a fixed amount at regular intervals — usually every month — instead of one lump sum. Each contribution buys into the market at that month's price, so you average your entry cost over time (pound-cost averaging) and let compounding work on every instalment.
SIP vs lump sum — which is better?
A lump sum invested early has the most time to compound, so with a steadily rising market it usually ends higher. A SIP suits money you earn month to month, smooths out volatility and removes the pressure to time the market. This tool lets you compare both modes with the same return and period.
How is the SIP future value calculated?
Each monthly amount P grows at the monthly rate i = annual return ÷ 12. Summing the growth of every instalment gives FV = P × ((1+i)^n − 1) / i × (1+i), where n is the number of months. We model contributions at the start of each month (annuity-due), the standard SIP convention.
What is a step-up SIP?
A step-up (or top-up) SIP raises your monthly amount by a fixed percentage every year — say 10% — so your investing keeps pace with your rising income. Even a small annual step-up markedly increases the final value, because the extra money also compounds. Set it in the step-up field.
What return should I assume?
Use a realistic long-run figure for your assets, not a best case. Historically a globally diversified equity portfolio has returned roughly 5–8% a year after inflation over long periods, bonds less. The calculator uses whatever nominal rate you enter — lower it if you want a cautious estimate.
Are these returns guaranteed?
No. Markets rise and fall, and past performance does not predict the future. The result is a projection based on a constant assumed return; real returns are uneven and your capital can go down as well as up. Treat the figure as a planning guide, not a promise.
Does it account for inflation, tax and fees?
No — it shows the nominal value. For purchasing power, subtract inflation (or enter a lower 'real' return). Remember fund charges and platform fees reduce returns, and in the UK gains outside an ISA or pension may be taxed. Investing through a Stocks & Shares ISA shelters growth from UK tax.
How much does starting early matter?
A great deal. Because growth compounds, the first years of a long SIP contribute disproportionately to the end value. Starting a 10-year head start can beat investing twice as much later — time in the market is the biggest single lever.
What does the year-by-year table show?
Each row is one year: the total you have invested by then, the growth earned to date, and the end-of-year value. The bars split every year into your contributions and investment growth, so you can see the crossover point where growth starts to exceed the money you put in.
Is this a mutual-fund or index-fund calculator?
It works for any regular or one-off investment where you assume an annual return — index funds, mutual funds, ETFs, a pension or a Stocks & Shares ISA. It does not fetch live fund prices; you supply the expected return, which keeps the projection transparent.