Compound interest calculator
Where today’s balance lands after years of contributions — and how much of the final number you never had to earn.
Balance in 20 years
€313.776
You contribute €145.000 and compounding adds €168.776 on top — 54% of the final balance is growth you never had to earn.
You contribute
€145.000
Compounding adds
€168.776
Safe income at 4%
€1.046/mo
A projection is a line. Your balance is a fact.
Track your accounts and the real line draws itself next to this one, month by month — across 31 currencies, without a bank login.
What compound interest actually does
Each month this calculator grows the balance by one twelfth of your annual return, then adds your contribution. Do that for long enough and the returns start earning returns of their own — which is why the line curves upward instead of running straight.
The dashed line on the chart is the same money with no return at all. The gap between the two is the entire case for investing rather than saving, and it is small for years before it becomes the majority of the balance. That shape is the reason time in the market is worth more than the size of any single contribution.
Nominal returns and the inflation trap
The default 6% is a nominalreturn — before inflation. It produces a big, satisfying number that will not buy what it appears to. Global equities have historically returned around 7% nominal and closer to 5% after inflation, and over 30 years that difference is not a detail: it is roughly half the final figure in today's money.
There are two honest ways to handle it. Use a nominal return and remember the result is in future money, or subtract your inflation assumption and read the result as today's money. The second is usually more useful, because it is the only one you can compare to what you spend now. Our FIRE calculator takes that second approach by default.
Why the last five years matter most
Try the "stay invested five more years" scenario. On a long projection it typically adds more than doubling your monthly contribution would, because those years compound the largest balance you will ever have.
This is also the argument against interrupting a plan. Money withdrawn early does not just cost you its own value — it costs every year of compounding it would have had. The practical answer is a cash buffer sized so you never have to sell, which is what the emergency fund calculator is for.
Common questions
Monthly. Each month the balance grows by one twelfth of the annual return, then your contribution is added. Compounding monthly rather than annually is how investment accounts actually behave, and it produces a slightly higher result than a yearly formula.
Either, as long as you read the answer the same way. A nominal return gives a balance in future money; subtracting your inflation assumption gives it in today’s money, which is usually more useful because it is comparable to what you spend now.
Global equities have historically returned roughly 7% nominal and about 5% after inflation over long periods, though any individual decade can look nothing like that. Lower is the conservative choice — a projection that disappoints is far less costly than one that misleads.
It is the same contributions with no return at all. The gap between the two lines is what compounding contributed, and watching it stay small for years before it dominates is the clearest argument for starting early and not interrupting.
Any of the 31 NetWorthTrackr supports. The calculator changes the symbol and digit grouping only — it never converts your figures.
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Estimates only, not financial advice. Every figure is calculated in your browser from what you typed — nothing is sent to us and nothing is stored.All tools →