Learn how to calculate simple interest with step-by-step instructions using the formula I=prt. Simply defined, interest equals principle times rate times time. The video shows various examples of calculating this formula by plugging different variables into the equation. Although, these calculations can seem hard to follow, the way they are presented is straightforward and simple to understand. The video also explains converting percentages to decimals, which is the cornerstone of applying this very useful, and invaluable interest formula.