This calculator requires the use of Javascript enabled and capable browsers. This script demonstrates the methodology of simple interest (as opposed to compound interest) and calculates interest (I) based on the principal (P), annual interest rate (r) and time (t). This particular calculator also allows, if any number is in the days field, the choice of how many days are in the year. The formula is (as designated in the calculator), Interest (I) = Principal (P) x Annual Rate (r) x Time (t), or I=P*r*t.

Enter the principal amount in dollars and cents. Enter the annual rate as a whole number, for instance, 3 is the equivalent of 3% (while it IS legitimate to enter a decimal in the case of 3.5 is 3 and a half percent). The time is typically in years but you may enter any accumulative combination of years, months and days. The number of days in a year is not a factor unless the days field is greater than zero (0). Click the Calculate button; read the simple interest. You may click on Clear Values and do another. Based on the previous instructions, you MAY enter a decimal for data in any of the fields but do not enter any commas or dollar signs (, or $).