📈 Compound Interest Calculator

See how your savings snowball when interest starts earning interest of its own.

How it works

Compounding means you earn interest on your interest, not just on the money you put in. The growth follows A = P × (1 + r/n)^nt, where P is your starting amount, r the yearly rate, n how many times a year interest is added, and t the number of years. Regular monthly deposits ride on top of that.

This calculator works month by month. It first converts your rate into an equivalent monthly rate — monthly rate = (1 + r/n)^n/12 − 1 — then grows the balance, adds your monthly contribution, and repeats. That is why daily or monthly compounding ends up slightly ahead of yearly compounding at the same stated rate.

An example

Say you start with $10,000, add $200 every month, and earn 7% a year compounded monthly for 20 years. Your savings would grow to $144,572.72. Of that, $58,000 is money you paid in — $10,000 at the start plus $48,000 of monthly deposits — and the remaining $86,572.72 is pure interest. Notice the interest ends up bigger than everything you contributed. That crossover is the whole point of starting early: in year one the balance only reaches $13,201.42, but the later years do the heavy lifting.

Common questions

How often should my money compound?

The more often, the slightly better. Daily compounding beats monthly, which beats yearly — but at normal savings rates the gap is small. A higher rate or a bigger monthly deposit matters far more than the compounding frequency.

Why does the interest grow so fast near the end?

Because the base keeps getting bigger. In the last years you are earning 7% on a six-figure balance instead of on your original $10,000, so each year adds much more than the year before.

Does this include tax or inflation?

No. The result is the raw growth before tax, account fees and inflation. For a rough real-world picture, try lowering the rate by 2–3 points to stand in for inflation and see how the ending balance changes.

Related calculators

This calculator gives estimates for learning. Rates, taxes and rules change, and your lender or the IRS has the final numbers — check big decisions against the real documents.