Enter the annual nominal rate and the number of compounding periods per year into the calculator to determine the effective interest rate.

## Effective Interest Rate Formula

The following formula is used to calculate an effective interest rate.

ER = (1 + i/n) ^ n – 1

• Where ER is the effective interest rate
• i is the nominal interest rate
• n is the number of compounding periods per year

## Effective Interest Rate Definition

An effective interest rate is defined as the nominal rate of interest when compounded over a number of periods per year.

## Effective Interest Rate Example

How to calculate an effective interest rate.

1. First, determine the nominal rate.

For this example, we will say we are looking at a credit card with a monthly nominal rate of .15 (15%).

2. Next, determine the compounding periods per year.

Since the nominal rate is per month, the compounding period is 12 months per year.

3. Finally, calculate the effective interest rate.

Using the formula above we find the effective rate to be (1+.15/12)^12 – 1 = .1607

## FAQ

What is an effective interest rate?

Effective interest is the true annual interest rate of a loan or credit based on a nominal rate and number of compounding periods per year. Interest compounds each period, so the more compounding periods the higher the effective rate will be.