Interest Calculator

Simple interest is calculated only on the principal amount — the original sum you invest or borrow. Compound interest is calculated on the principal plus all accumulated interest, leading to exponential growth. Over long periods, compound interest can produce significantly higher returns than simple interest, which is why it is often called "interest earning interest."

More frequent compounding (e.g., monthly vs. annually) results in higher returns because interest is earned on interest more often. For example, $10,000 at 5% over 10 years grows to $16,386 with annual compounding but $16,486 with monthly compounding — a difference of $100. The more frequently interest compounds, the closer it gets to continuous compounding.

The compound interest formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate, n is the compounding frequency per year, and t is the number of years. For simple interest, the formula is A = P(1 + rt). Understanding these formulas helps you see why compound interest accelerates your interest growth over time — each compounding period adds to the base on which future interest is calculated. This is why savings accounts with daily compounding outperform those with annual compounding, even at the same nominal rate.

Several factors can cause discrepancies. First, banks may use a different compounding frequency than what you assumed — some advertise annual rates but compound monthly or daily. Second, banks often quote an Annual Percentage Yield (APY) that already includes compounding effects, while the nominal rate shown on promotional materials does not. Third, fees, minimum balance requirements, or tiered rates can reduce your actual earnings. Always compare the APY, not just the nominal rate, when evaluating interest growth across different financial products.

Use the calculator in reverse: enter your target future amount as the desired result and solve for the principal. For example, if you want $50,000 in 20 years at 6% annual interest compounded monthly, you would need to start with approximately $15,200. This reverse calculation is invaluable for retirement planning, education savings, or any long-term financial goal. The key insight is that compound interest rewards early and consistent contributions — starting to save just five years earlier can reduce the required principal by nearly half.