Interest Rate Calculator
Solve for the interest rate given principal, final amount and time.
If you know how much you started with, how much you ended up with, and how long it took, you can work backward to find the implied interest rate — useful for evaluating an investment or loan after the fact.
Simple vs. compound rate — two different answers
This shows both a simple annual rate (assuming linear growth) and a compound annual rate (assuming growth compounds each year) — for most real investments and loans, the compound figure is the more accurate representation of the actual return.
Frequently asked questions
Why do I get two different rates from the same numbers?
Simple and compound interest describe growth differently — over multi-year periods, they diverge more, so check which method matches how your specific investment or loan actually calculates interest.
Can this show a negative rate?
Yes — if your final amount is less than your starting amount, the calculated rate will be negative, reflecting a loss.