Simple Interest Calculator
Calculate simple interest — interest earned or owed only on the original principal, with no compounding.
How this calculator works
Unlike compound interest, simple interest is calculated only on the original principal — it doesn't earn interest on previously accumulated interest.
I = interest · P = principal · r = annual rate (decimal) · t = time in years
When simple interest is actually used
Most everyday financial products — mortgages, credit cards, most savings accounts — use compound interest, not simple interest. Simple interest shows up more often in specific contexts: some short-term or add-on loans, certain bonds, and basic educational examples of how interest works.
Because compound interest almost always results in more total interest (or growth) than simple interest over the same period, it's worth checking which method actually applies to any real financial product you're evaluating.
A worked example
$8,000 at 4% simple interest for 5 years: interest is 8,000 times 0.04 times 5, or $1,600, for a total amount of $9,600.
Compare that to the same $8,000 at 4% compounded annually for 5 years, which would grow to roughly $9,733 — about $133 more, illustrating the gap between simple and compound interest even at a modest rate over a short period.
Where simple interest is actually used
While most everyday borrowing and saving compounds, simple interest still shows up in specific contexts: some short-term personal loans, certain promissory notes, add-on interest auto loans, and basic bond interest calculations all use simple interest structures.
Understanding the difference matters when comparing loan offers — a simple-interest loan and a compound-interest loan with the same stated rate can have meaningfully different total costs, especially over longer terms.
Frequently asked questions
What's the difference between simple and compound interest?
Simple interest only accrues on the original principal. Compound interest accrues on the principal plus previously earned interest, so it grows faster over time.
Where is simple interest commonly used?
Some short-term loans, certain bonds, and basic savings calculations use simple interest, though most bank accounts and investments compound.
Does simple interest ever result in more money than compound interest?
No — for the same principal, rate, and time period, compound interest always produces equal or greater growth than simple interest, since it earns returns on previously accumulated interest.
How do I know if my loan uses simple or compound interest?
Check your loan agreement or ask your lender directly — most consumer loans, especially mortgages and credit cards, use some form of compound interest, but it's always worth confirming.
Is simple interest better or worse for borrowers?
For loans, simple interest is generally better for the borrower than compound interest at the same rate, since it doesn't accumulate interest on previously accrued interest.