Enter a principal, annual interest rate, time period, and compounding frequency to compare simple interest against compound interest.
How to Use the Interest Calculator
One set of inputs — principal, rate, time, compounding frequency — gets computed two ways at once, so the simple and compound results sit side by side instead of needing two separate calculators.
Same principal, same rate, same time — simple and compound interest still land on different totals, and the gap between them is the entire reason "compound interest" gets talked about as if it's a separate force of nature.
Simple: I = P × r × t
Compound: FV = P(1 + r/n)ⁿᵗSimple interest is charged only on the original principal, every period, forever — a flat, linear rate of growth. Compound interest is charged on the principal plus whatever interest has already accumulated, so growth accelerates over time instead of staying flat. The longer the time horizon, the bigger the gap between the two totals gets, which is why compounding matters more for a 30-year investment than a 3-month loan.
Side by side below, both are computed from the exact same inputs so the difference is easy to see directly.