Investment growth calculator
Put in what you have and what you add each month. See what it becomes, and how much of that you never paid in.
What you already have, if anything.
A starting point, not a forecast. Change it and watch how much the answer moves.
More options(5)
Fund charge plus platform charge. Comes straight off the return.
Used only to show what the pot is worth in today's money.
Increases the monthly amount once a year, the way a pay rise would.
After 25 years, if returns average 7%
$201,188
Putting in $250 a month on top of $1,000 you already have, you would pay in $76,000 in total. The other $125,188 — 62% of the final pot — is growth you never contributed.
- You pay in
- $76,000
- Growth on top
- $125,188
- Growth as a share of the pot
- 62%
If returns average…
Nobody knows which of these happens
| Assumption | Final pot | Of which growth |
|---|---|---|
| 4% a year — cautious | $129,878 | $53,878 |
| 7% a year — middle | $201,188 | $125,188 |
| 10% a year — optimistic | $319,166 | $243,166 |
Markets do not return the same amount every year. The band shows the same plan under three different assumptions, so you can see how much the answer depends on a number nobody knows.
What this actually calculates
Three things are happening at once, and it is worth separating them. Your starting amount grows. Each monthly contribution starts growing from the day it lands. And the growth itself grows — the return earned in year three earns its own return in years four through thirty. That third part is compounding, and it is the only reason the curve bends upward rather than running straight.
The shaded area under the dashed line is money you paid in. Everything above it is the third part. For a typical thirty-year run, the money you never contributed ends up being most of the pot — which is the single most useful thing this chart tells you.
Why the number here differs from other calculators
Two deliberate choices, both of which make the answer slightly smaller and considerably more honest.
Contributions land at the end of each month. That is how a standing order works: you set it up, and the first payment sits for zero days before the month closes. Calculators that credit contributions at the start of the period quietly hand you an extra month of growth on every single payment.
An annual rate is converted properly. If you type 7%, this site uses the monthly rate that compounds to exactly 7% over twelve months. Dividing 7% by twelve, which is common, actually compounds to 7.23% — small in year one, and worth thousands over thirty.
The assumed return is the whole ballgame
Drag that slider between 5% and 9% and watch the final figure move by an enormous margin. This is not a flaw in the tool; it is the actual shape of the problem. Nobody knows what the next thirty years return, which is why every result on this site is shown at three different assumptions rather than one.
If you take one thing from this page, make it this: treat the output as a consequence of an assumption you chose, not as a projection of your future. The arithmetic is exact. The input is a guess. More on why that matters.
Things this deliberately ignores
- Tax. Rules differ by country, account type and income, and a wrong tax assumption is worse than none. Run the numbers gross and apply your own situation.
- The order of returns. The curve here is smooth. Real ones are not, and while the order barely matters when you are only paying in, it matters enormously once you start withdrawing.
- Whether any of this is a good idea for you. That is a question about your circumstances, not about arithmetic.
Common questions
What return should I put in?
Does it handle fees?
What does "in today’s money" mean?
Is my data stored?
Not advice. This tool applies arithmetic to assumptions you entered. It does not know your circumstances, your tax position or your goals, and it is not a recommendation to buy, sell or hold anything. Past returns do not predict future ones, and no figure here is a forecast.