R r 100. The simple interest formula. Input principle amount in some variable say principle.
Simple interest is calculated only on the original sum of money which is known as the principal.
Then fill in what you know to find the rate. R R100 R Rate of Interest per year as a percent. R r 100 t Time Period involved in months or years. From the base formula A P 1 rt derived from A P I and I Prt so A P I P Prt P 1 rt Note that rate r and time t should be in the same time units such as months or years.