Compound interest calculator

How much will you have if you invest every month? A lump sum now, a little every month, and time doing the work. No sign-up, nothing stored.

For reference, global stocks have returned around 7% a year on average over the very long run, with −40% years along the way. A savings deposit, far less.

140.204 in 20 years

What you put in What the return adds

You put in
58.000
Return
82.20459%
In today's money
94.353

“In today's money” takes off 2,0% inflation a year: it is what that money would buy at today's prices.

How it growsWhat you put in, what it is worth and what it is worth in today's money
0 50.000 100.000 150.000 200.000 year 0year 10year 20

What you put in Value In today's money

What each year addsFrom year 8 on, the year's return adds more than you do.
0 5.000 10.000 15.000 20.000 Year 1: you put in 2.400 and the return adds 776 Year 2: you put in 2.400 and the return adds 998 Year 3: you put in 2.400 and the return adds 1.236 Year 4: you put in 2.400 and the return adds 1.491 Year 5: you put in 2.400 and the return adds 1.763 Year 6: you put in 2.400 and the return adds 2.055 Year 7: you put in 2.400 and the return adds 2.366 Year 8: you put in 2.400 and the return adds 2.700 Year 9: you put in 2.400 and the return adds 3.057 Year 10: you put in 2.400 and the return adds 3.439 Year 11: you put in 2.400 and the return adds 3.848 Year 12: you put in 2.400 and the return adds 4.285 Year 13: you put in 2.400 and the return adds 4.753 Year 14: you put in 2.400 and the return adds 5.254 Year 15: you put in 2.400 and the return adds 5.790 Year 16: you put in 2.400 and the return adds 6.363 Year 17: you put in 2.400 and the return adds 6.976 Year 18: you put in 2.400 and the return adds 7.633 Year 19: you put in 2.400 and the return adds 8.335 Year 20: you put in 2.400 and the return adds 9.086 year 1year 10year 20

What you put in What the return adds

Year by year
YearYou put in ReturnValue In today's money
1 12.400 776 13.176 12.918
2 14.800 1.774 16.574 15.931
3 17.200 3.011 20.211 19.045
4 19.600 4.502 24.102 22.266
5 22.000 6.265 28.265 25.600
6 24.400 8.319 32.719 29.054
7 26.800 10.686 37.486 32.634
8 29.200 13.386 42.586 36.347
9 31.600 16.443 48.043 40.200
10 34.000 19.882 53.882 44.202
11 36.400 23.730 60.130 48.360
12 38.800 28.015 66.815 52.683
13 41.200 32.768 73.968 57.180
14 43.600 38.022 81.622 61.859
15 46.000 43.811 89.811 66.731
16 48.400 50.174 98.574 71.806
17 50.800 57.150 107.950 77.094
18 53.200 64.783 117.983 82.607
19 55.600 73.118 128.718 88.356
20 58.000 82.204 140.204 94.353

How it is calculated

How is compound interest calculated?

Each month, what you already have grows at the equivalent monthly return and, at the end of the month, the contribution is added. The monthly return is the one that, repeated twelve times, gives exactly the annual % you entered: (1 + r) to the power of 1/12, minus 1. That way the return on the return also works, which is why the light bar grows faster and faster.

Why does time matter more than the %?

€200 a month for 30 years at 7% comes to about €234,000, of which you put in 72,000. The same €200 for 15 years comes to about 62,000. Half the time does not give half the money: it gives a quarter, because the last years are the ones that grow most.

What does this calculator NOT measure?

No market returns the same % every year. This is arithmetic, not a forecast: the real path will have good years and bad years, and the end result may land above or below. Nor does it take off fees or taxes, which over the long run eat a sizeable share.

How does inflation affect it?

A million thirty years from now does not buy what a million buys today. The “in today's money” column divides each year by cumulative inflation, so you see purchasing power and not just the number.

And then, track it for real

Log your contributions in Arvenyx and you see the real return you are getting and whether you are on the path you set.

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