Overview
Enter a starting principal, a target future value, a time period in years, and a compounding frequency to solve for the annual interest rate (r) that would produce that growth: r = n × ((A/P)^(1/(n × t)) − 1), where A is the target future value, P is the principal, n is the number of compounding periods per year, and t is the number of years. This is the inverse of the standard compound-interest formula used by this site's Compound Interest Calculator - instead of projecting a future value from a known rate, it works backward from a known starting and ending amount to find the rate that connects them. Useful for checking what return an investment would have needed to reach a specific goal, or reverse-engineering an advertised growth claim. Runs entirely client-side, and this is an informational estimate, not financial advice.
Best for: Figuring out what annual return an investment would have needed to grow from a starting amount to a target amount
How to use this tool
- Enter the principal and target future value. The starting amount and the ending amount you want to solve the rate for.
- Enter the time period and compounding frequency. How many years the growth happened over, and how often interest compounds.
- Read the required rate. The annual interest rate that connects the principal to the target future value, using r = n × ((A/P)^(1/(n×t)) − 1).
Frequently asked questions
The Compound Interest Calculator solves for the future value given a known rate. This tool solves the opposite problem - given a known starting amount, ending amount, and time period, it works backward to find what rate would explain that growth. They're inverse operations built on the same underlying formula.
The tool reports an error rather than a nonsensical result - this compounding model solves for a positive growth rate connecting a smaller starting amount to a larger ending amount, and a decline isn't expressible as a compounding rate in this formula.
The same total growth can be explained by different nominal rates depending on how often that rate is assumed to compound - a rate that compounds daily needs to be slightly lower than one that compounds annually to produce the identical ending balance, since more frequent compounding does more of the work on its own.