A interest helps you calculate interest values accurately and instantly.
Calculate simple or compound interest and see your money grow.
An interest calculator computes how much money you earn (or owe) from interest, using either simple or compound interest formulas.
$10,000 at 5% simple interest for 3 years earns $1,500. With monthly compounding, it earns $1,616 — the power of compound interest.
Simple interest is calculated only on the original principal: Interest = P x r x t. Compound interest is calculated on both principal and accumulated interest: A = P(1 + r/n)^(nt). Compound interest grows faster over time.
For saving and investing, compound interest is better because your money grows faster. For borrowing, simple interest costs less. Most savings accounts and investments use compound interest, while some short-term loans use simple interest.
The Rule of 72 estimates how long it takes to double your money: Years to double = 72 / Interest Rate. At 8%, your money doubles in about 9 years. This is a quick approximation for annual compounding.