Convert a nominal interest rate to its effective annual rate, or solve backward from an effective rate to the nominal rate.

How to Use the Effective Interest Rate Calculator

Toggle between Nominal → Effective and Effective → Nominal depending on which rate you already have. Either mode also needs the compounding frequency — how many times per year interest is applied — since that number is what makes the two rates diverge in the first place.

Effective Rate = (1 + Nominal Rate ÷ n)ⁿ − 1
Nominal Rate = n × [(1 + Effective Rate)^(1/n) − 1]

n is the compounding frequency. Whenever n is greater than 1, the effective rate always comes out higher than the nominal rate — a nominal rate only states the annual rate before compounding gets applied within the year, while the effective rate accounts for interest earning interest on itself before the year is even over.

A nominal 6% compounded monthly, the calculator's default, works out to an effective 6.1678% — not a rounding error, but interest paid in month one earning its own interest for the remaining eleven months, and so on for every month after. That's exactly the gap that makes rate comparisons deceptive on paper: "6% compounded monthly" and "6.1% compounded annually" look close enough to call a wash at first glance, but the monthly-compounding rate is already earning more before anything else about the two offers gets accounted for.

The practical takeaway cuts both ways: as a saver, the account advertising more frequent compounding is doing you a real, if usually small, favor even at an identical nominal rate; as a borrower, that same frequent compounding works against you — which is exactly why regulators in many countries require lenders to disclose an effective or annual percentage rate alongside whatever nominal rate they advertise.