Compound interest calculator
Estimates a final balance using your starting amount, monthly contribution, interest rate and term.
Compounds month by month: the starting sum earns interest and your monthly contribution is added at the end of each month. You can see how much of the final figure is money you paid in and how much is interest.
- Enter your starting amount and monthly contribution
- Set the annual rate and the term
- Compare what you paid in, the interest and the final amount
A model calculation at a constant rate. Tax, fees and inflation are not included, and this is not investment advice.
Frequently asked
What does it cost?
Every tool shows its price before you start. Tools marked free run in your browser and never cost anything — no sign-up needed.
What happens if processing fails?
You are not charged. We only charge when a result is actually produced; if the run fails, the charge is reversed.
What happens to my files?
Uploaded files are processed in memory for that one request and then discarded. We do not store them, and their contents never reach our logs or analytics.
Do you use my own API key?
No. Your BYOK key belongs to the Playground and is never used for these tools.