Interest Rate Calculator

Know the start, the end, and the time — but not the rate? Solve for it directly.

Starting and ending amounts

Starting amount

Ending amount

Time

years

Required annual rate

7.18%

This is the constant, compounding annual growth rate that turns the starting amount into the ending amount over the time you set — useful for checking whether a past investment, or a future goal, implies a realistic rate of return.

A worked example

Turning $10,000 into $20,000 over 10 years — doubling your money — requires a constant annual rate of about 7.18%, not the 10% a quick mental shortcut (100% gain ÷ 10 years) might suggest.

Frequently asked questions

When is this calculator actually useful?

Whenever you know a starting amount, an ending amount and how long it took, but not the rate — for example, checking what annual return a past investment actually delivered, or what rate a savings goal implicitly requires.

Does this assume the rate stayed perfectly constant?

Yes — it solves for the single constant rate that would produce the same result. Real investments fluctuate year to year, so this is the equivalent steady rate (similar to a CAGR), not necessarily what happened in any individual year.

This calculator provides estimates for general informational purposes only and is not financial advice.