Simple Interest Calculator
Interest on the original principal only, with no compounding.
Every calculation runs locally in your browser. Nothing you enter here is sent to a server or stored anywhere.
Interest earned
$150
Total amount
$1,150
For informational and educational purposes only — not financial, investment, or tax advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
Simple interest vs. compound interest
Simple interest is calculated only on the original principal for every period — interest earned in year one doesn't itself earn interest in year two. That makes the math a straight line: interest = principal × rate × time. Compound interest, by contrast, earns interest on previously earned interest, which is why it grows faster over long periods. Simple interest shows up in some auto loans, short-term notes, and certain bonds — for savings accounts and most investments, check our compound interest calculator instead.
Frequently asked questions
When is simple interest actually used?
Common in short-term loans, some auto loans, certificates of deposit, and bonds — situations where interest is meant to accrue predictably on a fixed principal rather than compound.
What's the formula?
Interest = Principal × Rate × Time. Unlike compound interest, the interest earned each period is always based on the original principal, never on previously accrued interest.