when calculating simple interest, what must you do if you want to invest for months instead of years?

When calculating simple interest for an investment period measured in months instead of years, you must convert the time period from months to an equivalent fraction of a year. This is done by dividing the number of months by 12, since there are 12 months in a year. Then use this converted time value in the simple interest formula I=P×r×tI=P\times r\times tI=P×r×t, where ttt is now the time in years as a decimal. For example, if investing for 9 months, convert it to years as 912=0.75\frac{9}{12}=0.75129​=0.75 years, then apply the simple interest formula with t=0.75t=0.75t=0.75.