Compound Interest Calculator

The standard formula is FV = P × (1 + r/n)^(n×t), where P is the principal, r is the annual interest rate (as a decimal), n is the number of compounding periods per year, and t is the number of years. This calculator applies this formula automatically as you adjust inputs.

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any interest already earned. Over long periods, this difference becomes dramatic — compound interest can produce returns many times larger than simple interest at the same rate.

More frequent compounding always produces a higher return. Daily compounding yields slightly more than monthly, which yields more than annual. For most savings accounts and fixed deposits, monthly or quarterly compounding is standard. The practical difference between daily and monthly is small — but over 30 years it can add up.

The basic mode calculates growth on a lump-sum principal. Switch to the "With Contributions" mode to model regular monthly additions — useful for dollar-cost averaging into a savings account, brokerage or retirement plan where you add a fixed amount each month.

It uses the standard compound interest formula (FV = P(1 + r/n)^nt) with full floating-point precision. Results are rounded to 2 decimal places for display. Real-world returns may vary due to taxes, fees, and variable interest rates — this calculator assumes a fixed rate throughout the period.