Tools › Compound interest calculator
See how a starting balance plus regular contributions grows over time, with daily, monthly, or yearly compounding.
Compound interest earns returns on both your original money and the returns it has already earned. Because each period’s interest is added to the balance before the next period is calculated, growth speeds up the longer you leave it — the effect people call “interest on interest.” Contributions add fuel: every deposit starts compounding from the moment it lands.
Start with $10,000, add $300 a month, and earn 6% a year compounded monthly. After 20 years the balance is far more than the deposits alone, because two decades of monthly compounding do most of the work in the final years — which is why starting early matters more than the exact rate.
Compound interest is calculated on both your original principal and the interest already added. Each period, interest is applied to the running balance, so growth accelerates over time.
Yes. More frequent compounding (daily vs yearly) produces a slightly higher balance because interest is added to the balance more often.