Compound Interest Calculator

Compound Interest Calculator is a free online tool that calculates the future value of an investment or savings deposit using compound interest. Enter the principal amount, annual interest rate, compounding frequency, and time period — the tool shows the total amount, total interest earned, and a year-by-year growth breakdown.

Compound interest is the process of earning interest on both the original principal and the accumulated interest from previous periods. It is the fundamental mechanism behind long-term wealth accumulation and is why Albert Einstein reportedly called it "the eighth wonder of the world." Unlike simple interest (calculated only on the principal), compound interest grows exponentially over time.

The compounding frequency determines how often interest is calculated and added to the principal. Annual compounding calculates interest once per year. Monthly compounding calculates it twelve times per year, resulting in slightly higher effective returns because each month's interest starts earning interest sooner. Daily compounding, common in savings accounts, compounds every day. More frequent compounding produces marginally higher returns — daily versus monthly makes a small but real difference over long time horizons.

The Rule of 72 is a useful mental shortcut: divide 72 by the annual interest rate to estimate the number of years it takes to double an investment. At 6% annual return, your money doubles in approximately 12 years (72 ÷ 6). At 9%, it doubles in 8 years. At 12%, in 6 years. This illustrates both the power of time and the outsized impact of rate differences over long periods.

Compound interest works against you in debt scenarios. Credit card debt compounding at 36% per annum doubles in just 2 years (72 ÷ 36). Understanding the compounding mechanics of both savings and debt is one of the most financially valuable pieces of knowledge an individual can have.