Not every loan or investment compounds. Our simple interest calculator uses the plain, non-compounding formula that some short-term loans, bonds, and promotional financing offers actually rely on.
The formula
Interest = Principal × Rate × Time
Total = Principal + InterestNo exponents, no compounding periods — just a direct multiplication. This is exactly why simple interest was historically easy to calculate by hand, long before calculators were common.
Example
$10,000 principal, 5% annual rate, 3 years:
Interest = 10,000 × 0.05 × 3 = $1,500
Total = 10,000 + 1,500 = $11,500Simple vs compound interest
Simple interest calculates interest only on the original principal for the entire period — you never earn or pay interest on previously accumulated interest. Compound interest recalculates on the growing balance at each period, producing a larger total for the same nominal rate over time. Most mortgages, credit cards, and savings accounts actually use compound interest — check your specific loan or account terms, and use our compound interest calculator if compounding applies to your situation.
Where simple interest is actually used
Certain short-term loans, some bonds, and promotional “0% interest for 12 months” style financing sometimes use simple interest calculations. Fractional years work fine too — enter 0.5 for six months or 2.5 for two and a half years, since the formula scales linearly with time.