Calculator
Enter what you have today, what you can add each month, and how many years you are willing to give it. You get two figures back, kept separate: how much you put in, and how much time put in.
Estimated final value
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An estimate, not a forecast: markets do not deliver the same return every year.
The calculator compounds month by month. Each month it multiplies the balance by the monthly return (the annual figure divided by twelve) and then adds your contribution:
balance = balance × (1 + annual return / 12) + contributionRepeated once for every month in your horizon. The figure shown as "generated by compounding" is simply the final value minus everything you put in, and it is the part you would not have had by leaving the money still.
It depends what you invest in, and nobody can know it in advance. As a historical reference, a global equity portfolio has run around 7–8% nominal a year over very long periods, and a mixed portfolio with bonds considerably less. The useful move is not guessing the right figure but trying three of them, pessimistic, middling and optimistic, and checking whether your plan still stands up under the pessimistic one.
Because growth is not linear. The last years work on the largest balance, so they contribute far more than the first ones. This is why starting earlier is worth more than contributing more: a year of delay does not remove your first year, it removes your last.
No. They are nominal. To think in today’s purchasing power, subtract your inflation expectation from the return you enter: 7% with 2.5% inflation is roughly 4.5% real. The result is then already in today’s money.
No. The whole calculation runs in your browser in JavaScript; nothing is sent to a server and nothing is stored. You can verify it by turning off your network and using the calculator anyway.