Compound growth calculator
Put in what you have, what you can add each year, and a return you think is realistic. It shows how much of the final figure is money you contributed and how much is growth — which is usually the surprising part.
Asset growth projection
See how a starting amount and regular contributions compound over time, in USD.
This is arithmetic on the numbers you enter, not a forecast. The return you type is an assumption, not something anyone can promise — real returns vary year to year and can be negative. Interest is applied to the balance at the start of each year and your contribution is added at the end, which is the conventional method and affects the result. Inflation, fees and tax are not deducted.
InvestWise4U provides interactive financial calculators and data modelling for educational and informational purposes only. Content does not constitute personalised financial, investment, or legal advice. Figures are projections from assumptions you choose, not forecasts, and no return shown is guaranteed. Read the full disclaimer.
How this calculator works
Compound growth is one line of arithmetic repeated once per year. Each year the balance earns the return you chose, then your contribution is added on top, and the new total becomes the starting point for the following year.
Two details matter for reading the output honestly. Interest is applied to the balance at the start of each year, and your contribution lands after it — so money paid in during year five begins earning in year six, not immediately. That is the conservative way round, and it means the figures here will be slightly lower than a calculator that assumes you invest everything on 1 January.
The rate is annual and applied once a year, not monthly. A product quoting a monthly or daily compounding rate will run marginally ahead of this projection; the gap is small over short horizons and widens over decades.
What the three colours mean
Each bar separates the total into the part you started with, the part you added, and the part the market produced. That third section is the only one you did not fund yourself, and watching when it overtakes the other two is the whole point of the chart.
Worked examples
The arithmetic is easier to trust once you have seen it produce a number you can check. Each example below uses an 8% annual return — the long-run historical average often quoted for broad equity indices, and an assumption rather than a promise.
Starting from nothing, £200 a month
£2,400 a year for 30 years is £72,000 of your own money. At 8% the projection ends near £272,000. Roughly three quarters of the final figure is growth rather than contribution — and none of it arrives in the first decade, which is where most people give up.
A £10,000 lump sum, left alone
With no further contributions, £10,000 at 8% doubles in roughly nine years and reaches about £100,000 after 30 years. The doubling period is the useful thing to carry around: divide 72 by your rate of return and you get the approximate number of years to double, which at 8% is nine.
The cost of waiting five years
Someone contributing £200 a month for 30 years ends near £272,000. The same person starting five years later, and contributing for 25, ends near £175,000— about £97,000 less for £12,000 fewer contributions. The missing years are the earliest ones, and those are the years each pound spends longest compounding.
This is the single most useful thing the calculator demonstrates: the penalty for delay is far larger than the penalty for contributing less.
Key factors and limitations
It assumes a steady return, and markets are not steady
The projection applies the same percentage every year. Real markets deliver that average as a sequence of good and bad years, and the order they arrive in changes the outcome — severely so once you start withdrawing, because a fall early in retirement forces you to sell more units to fund the same income.
It ignores fees
Platform charges and fund expense ratios come out before you see a penny. A 1% annual fee against an 8% return is not a 1% reduction in your final total — compounded over 30 years it removes roughly a quarter of it. Check the expense ratio of anything you buy and subtract it from the rate you enter here.
It ignores tax
Dividends and gains are taxable in most jurisdictions unless held inside a tax-advantaged wrapper such as an ISA or a Roth IRA. Returns inside a wrapper compound undiminished; returns outside one are reduced every year, and that reduction compounds against you exactly as growth compounds for you.
It ignores inflation
Every figure is in nominal terms — the number your statement will show, not what it buys. Over 30 years at 3% inflation, a pound keeps about 40% of its purchasing power — the projection does not shrink, but what it buys does. The inflation-adjusted simulator runs the same projection and shows both lines together.
Inputs are bounded on purpose
The return accepts 0–50% and the horizon 1–50 years. Beyond those the output stops being a projection and becomes a fantasy, and a calculator that cheerfully compounds 400% for a century teaches the wrong lesson.
Frequently asked questions
- What return should I use?
- There is no correct answer, which is why the field is yours to set. Broad equity indices have historically averaged around 7–10% a year before inflation over long periods, government bonds and savings considerably less. Use a figure you could defend to someone sceptical, then try a lower one and see how much the conclusion changes.
- Does it compound monthly or annually?
- Annually. Interest is applied to the balance at the start of each year and your contribution is added afterwards. A product that compounds monthly will run slightly ahead of this projection.
- Why is my result lower than other calculators?
- Most likely because contributions here are added at the end of each year rather than the start, which is the more conservative assumption. Over long horizons the difference is modest, but it is real.
- Should I invest a lump sum or spread it out?
- Mathematically, investing a lump sum immediately wins more often than not, because the money spends longer in the market. Spreading it reduces the risk of committing everything just before a fall. The calculator shows the first effect; only you can price the second.
- Does this account for inflation, fees or tax?
- No. It projects nominal growth only. Fees and tax should be subtracted from the rate you enter, and inflation is handled by the inflation-adjusted simulator, which shows the same projection in today’s money alongside the nominal figure.
- Is this financial advice?
- No. It is an arithmetic tool for exploring assumptions you choose. It is not a recommendation, no return shown is guaranteed, and no product is being promoted. See the financial disclaimer for the full position.
Where to go next
Once the projection makes sense, the next question is what to actually buy — and that depends on where you live, how soon you need the money and how much volatility you can tolerate. Compare the options available in your market with their real minimums, fees and lock-in periods, or read how long it takes to reach a target at different contribution levels.