Compound interest calculator
Compound interest is what happens when interest earns more interest. Early on it barely shows, which is why many people give up; past a certain point it is most of the total. See where that point falls in your case.
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Your numbers
Change any field and the result updates instantly. Try adding five years and watch what happens.
You would have
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Fill in the fields to see your result.
- What you put in
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- What interest puts in
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- Real value (inflation removed)
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See it year by year
What compound interest is, and why it fools people
With simple interest, €10,000 at 7% earns €700 every year, always the same. With compound interest, the second year earns interest on €10,700, the third on €11,449, and so on. The difference looks small and in year one it is: €49. Over twenty years it is more than €10,000.
What fools people is that growth is a curve, not a straight line, and humans read curves badly. Almost everyone underestimates the long-run result, which is why the most expensive mistake is usually not picking the wrong place for the money, it is starting five years late.
Final amount = C₀ × (1 + i)ⁿ + A × [((1 + i)ⁿ − 1) ÷ i]C₀ is your starting amount, A the monthly contribution, i the monthly return (the annual figure divided by 12) and n the number of months. This calculator simulates month by month with contributions at the end of each month, which is the standard convention.
Why this one also shows you the real value
Most compound interest calculators hand you a huge final figure and stop there. The trouble is that the figure is in euros twenty years from now, and euros twenty years from now buy less than today's.
Enter an inflation rate and you will also see the real value: what that money would buy in today's terms. It is usually a useful splash of cold water. At 2% inflation, €100,000 in 20 years buys what roughly €67,000 buys today.
This is not meant to discourage. It is so the number you make decisions with is the right one. And it still beats leaving the money still, because idle money loses that same 2% without earning anything in return.
Picking a return without kidding yourself
Return is the field where it is easiest to lie to yourself. Type 15% and you get a beautiful number that means nothing.
For reference, a global equity index has historically averaged around 7% a year after inflation, with 30% drops along the way. A savings account or deposit sits far below that. Past returns do not guarantee future ones, and this calculator predicts nothing: it projects the assumption you type in.
- Always try two scenarios: the return you expect, and two points lower.
- For short horizons (under five years), use a conservative return, there is no time to recover from a bad year.
- Raise the monthly contribution before raising the expected return. It is the only one of the two you control.
From a projection to what actually happens
A projection is an assumption. What really changes the outcome is keeping the contribution going when markets fall, and not losing sight of what you have built up.
In Neto you can track funds, ETFs, shares and crypto with up-to-date prices, see how much you contributed versus how much it grew, and have it folded into your total net worth. It is not a broker and executes nothing: it just shows you where you stand.
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Frequently asked questions
How often does this calculator compound?
Monthly. The annual return you type is divided by 12 and applied each month, with contributions added at the end of each month. That is the standard convention and the one most funds use.
What annual return is realistic?
It depends entirely on where the money sits. A global index has averaged around 7% historically, a deposit far less, a current account nothing. No past figure guarantees a future one: the calculator projects your assumption, not a promise.
Why is the inflation-adjusted result so different?
Because they answer two different questions. Without inflation you see how many euros you will have; with it you see what you will be able to buy. For deciding how much to save, the second one is what matters.
Does it work for a pension or an index fund?
It works for any product where you contribute regularly and the return is reinvested. What changes between products is the return and the fees, subtract annual fees from the percentage you type in.
Is this investment advice?
No. It is a calculation tool. It does not recommend any product or suggest what to do with your money; it only projects the numbers you enter.
Do you store what I type?
No. Everything is calculated in your browser and nothing is sent to any server.