Investment Calculator
Project future value of investments with regular contributions
100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.
About this tool
The striking thing about long-term investing is how much of the final figure comes from contributions you have not made yet, growing for years you have not lived through. Someone saving £300 a month for 30 years at 7% contributes £108,000 and ends with roughly £366,000 - meaning about two thirds of the result is growth rather than deposits. Run the same numbers over 20 years instead and growth accounts for less than half. That is the whole argument for starting early stated numerically: the last decade of any long horizon does more work than the first two combined, because it compounds on everything accumulated before it. Two cautions belong alongside that. The rate you enter is a smooth average that no real market delivers - actual returns swing widely year to year. And a nominal projection ignores inflation, which quietly removes a large share of the purchasing power from any figure decades out. Calculations run in your browser.
How to use this tool
- Enter your starting amountWhatever you are beginning with, including zero if you are starting from nothing.
- Add your regular contributionThe monthly amount. Over a long horizon this usually matters more than the opening balance.
- Set the return rate and time horizonBe conservative with the rate. Try several time periods - the difference between 20 and 30 years is dramatic.
- Compare growth against contributionsSeeing how much of the total is growth rather than deposits is the most useful output.
How investment growth is calculated
Future value has two parts: the lump sum growing at the return rate, plus each regular contribution growing for the years it is invested. With yearly compounding, 10,000 invested at 6% for 20 years becomes about 32,000, and 2,400 a year (200 a month) added on top grows to about 88,300 - a total of roughly 120,000 from 58,000 of your own money.
Small changes to the rate or the timeline make a big difference, because growth compounds on growth. Use a realistic long-term return after fees, and remember that inflation reduces what the final figure will buy.
Key features
- Separates contributions from growth, which is the comparison that actually motivates saving.
- Handles regular contributions rather than lump sums only, matching how most people invest.
- Easy to compare time horizons side by side.
- Runs in your browser - your financial figures are never transmitted.
- No account and no lead capture.
Common uses
- Projecting retirement savings from a monthly contribution.
- Seeing what starting five years earlier is worth in the final figure.
- Setting a realistic monthly amount for a long-term goal.
- Comparing conservative and optimistic return assumptions.
- Explaining compound growth to someone deciding whether to start.
Tips for better results
- Use a conservative rate. A projection built on an optimistic assumption is a plan built on hope.
- Subtract inflation to see the result in today's money - 7% nominal with 3% inflation is about 4% real.
- Account for fees. A 1% annual charge compounds against you exactly as returns compound for you, and over decades it is substantial.
- Run 10, 20 and 30 years. The curve is much steeper at the end, and that shape is the argument for starting now.
- Increase contributions with income rather than leaving them fixed for thirty years.
Mistakes to avoid
- Assuming a steady annual return. Markets do not deliver a smooth average, and a bad sequence early on matters more than the average suggests.
- Ignoring inflation, which makes a thirty-year figure look far better than its actual purchasing power.
- Leaving fees out of the calculation, when they compound against the whole balance every year.
- Treating the projection as a promise rather than an illustration of how compounding behaves.
- Waiting to start until the amount available feels significant - time contributes more than the deposit size.
Frequently asked questions
This depends on your specific investment type and risk tolerance - historical stock market averages are sometimes used as a reference point, but actual future returns are never guaranteed and can vary significantly year to year.
The base calculation projects nominal future value based on your inputs - if you want to see the real (inflation-adjusted) value, you'd need to factor in an estimated inflation rate separately.
Yes, and over a long horizon those usually matter more than the opening balance. Consistent monthly investing is what produces most of the final figure for most people.
Over a long period, most of it. £300 a month for 30 years at 7% means £108,000 contributed and roughly £366,000 at the end - about two thirds is growth. Over 20 years the split is much closer to even, which is precisely why starting earlier matters.
Yes. A 1% annual fee compounds against your entire balance every year, so entering 6% rather than 7% is the honest way to model a fund charging 1%. Over decades the difference is large.
No. Everything is calculated in your browser and nothing is transmitted or used for lead generation.
Nominal return is the growth you see on the statement; real return is what is left after inflation. With 7% growth and 3% inflation, the real return is about 4% - a better guide to what the money will buy in the future.
Historically a lump sum invested at once has more often ended ahead, because markets rise more often than they fall. Monthly investing smooths the entry price and is easier to stick with. Use the calculator to compare both with your own figures.
A lot over decades. A 1% annual fee on a 30-year plan can take roughly a quarter of the final value compared with a 0.2% fund. Subtract the fee from your return rate to see the effect.