Compound Interest Calculator
See how an initial investment plus regular contributions grows with compounding returns over time.
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Total interest earned$0
How compound interest works
Compound interest is interest earned on both your original investment and on the interest that has already accumulated. Over long periods it is the single most powerful force in investing — each year's returns generate their own returns the following year.
The formula combines a lump-sum term and a contributions term. For a principal P, rate r, n compounds per year over t years, the lump sum grows to P(1 + r/n)nt, with regular contributions added as an annuity on top.
To go deeper on why time in the market matters more than timing it, read our guide on why a long time horizon is your biggest advantage.