Compound Interest Calculator
Initial amount, monthly contribution, rate and years. Monthly compounding, with the interest split out from what you paid in.
Final balance
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Total contributed
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Interest earned
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Growth multiple
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Worked example
Starting with 10,000 and adding 500 a month at 7% for 20 years ends near 264,000. You put in 130,000 of that; the rest is compounding.
Compounding is growth on growth. The first years look unremarkable — the balance barely moves away from what you contribute — and the last years do most of the work. This shape is why starting early beats contributing more later.
What the projection ignores
Inflation, taxes on gains, fees, and the fact that returns are not a constant 7% — they are volatile, and sequence matters. A single bad decade early cannot be averaged away by a good one late. Treat the output as a shape, not a forecast.