Use the simple interest formula: Rate = (Simple Interest × 100) / (Principal × Time)
Use the compound interest formula if needed: Rate = [((Amount / Principal)^(1 / Time)) – 1] × 100
Identify the principal amount
Identify the time period
Identify the interest earned or total amount
Substitute the known values into the correct formula
Solve for the rate
Express the rate as a percentage per year or per the given time period