Compound Interest Calculator
Watch your savings grow — like Ollie collecting pebbles, one month at a time.
Your cozy results
Ollie approves!
- Final balance
- Total contributions
- Interest earned
- Years
A note on returns
The annual return you enter is a long-term planning assumption for diversified stock investments (like index funds) — a projection, not a guaranteed rate. For context: cash savings currently earn around 4%, while the stock market has averaged about 10% a year before inflation (roughly 7% after) over the past century. Actual returns vary year to year, and past performance never guarantees future results.
Compound interest FAQ
How does compound interest work?
Compound interest means you earn interest on your interest. Each month, interest is added to your balance, and the next month you earn interest on the larger amount.
How often is interest compounded here?
This calculator compounds monthly, which is the standard for savings accounts and most investment projections.
Is the 7% rate realistic?
7% is a common long-term planning assumption for a diversified stock portfolio — not a guaranteed rate and not a bank deposit rate (cash savings currently earn around 4%). Historically the stock market has averaged about 10% a year before inflation. Past performance never guarantees future results.
Can I include monthly contributions?
Yes. Enter a monthly contribution to see how regular saving dramatically boosts your final amount.
What is the formula used?
FV = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)], with monthly compounding (n = 12).