Simple Interest Calculator
Calculate simple interest and the total amount due using I = PRT, and see how it differs from compound interest.
The rate is a percent per year (5 for 5%). Numbers stay in your browser. The default is 10,000 at 5% for three years, which is 1,500 of simple interest and a total of 11,500.
Quick answer: simple interest is principal × rate × time. With the principal in B2, the annual rate in C2 (as 5% or 0.05) and the years in D2:
=B2*C2*D2
=B2*(1+C2*D2)The first cell is the interest only; the second is principal plus interest. This is not the same as the compound interest FV formula, and it is not a CAGR.
$10,000 at 5% for three years
Interest is 10,000 × 0.05 × 3 = 1,500, and the total is 11,500. In Google Sheets on 12 November 2026, =10000*0.05*3 與 =10000*(1+0.05*3) returned those exact figures. A zero rate for the same principal and term, =10000*0*3, returned 0.
Time can be a fraction of a year. 5,000 at 6% for six months is =5000*0.06*0.5, which returned 150, so the total is 5,150. If you prefer months, use years as months ÷ 12 rather than changing the formula.
Why this is smaller than compound interest
Simple interest never adds the earned interest back into the base. The same $10,000 at 5% for three years, compounded monthly, grows to 11614.722313334678 on the compound interest calculator — about $115 more than the 11,500 simple total. The gap widens as the term gets longer or as compounding gets more frequent. Use this page only when the agreement really is simple interest (some short-term loans and some teaching examples). If interest is added to the balance, use FV.
The rate still has to be entered as 5% or 0.05, not 5, or you will compute 500% a year. Taxes, fees, and a rate that changes mid-term are not in I = PRT.
Questions that come up
What is the simple interest formula in Excel or Google Sheets?
With the principal in B2, the annual rate in C2 (as 5% or 0.05) and the time in years in D2, interest is =B2*C2*D2 and the total is =B2*(1+C2*D2).
How is simple interest different from compound interest?
Simple interest is charged only on the original principal. Compound interest is charged on principal plus interest already earned. $10,000 at 5% for three years is $1,500 of simple interest (total $11,500) but $11,614.72 if that same 5% is compounded monthly.
Can the time be a fraction of a year?
Yes. Six months is 0.5 in the same formula. 5,000 at 6% for half a year is $150 of simple interest.