Compound Interest Calculator

See how your savings or investment grow over time with compounding interest.

InvestmentsBusiness

Currency

Initial Investment $

Annual Interest Rate %

Time Period (years)

Monthly Contribution (optional) $ / mo

Compounding Frequency

Inflation Rate (optional) %

Fill in the form and press "Calculate" to see the result.

Results are informational. Calculation is based on your input and public rules, official accounting may differ. For accuracy, confirm the final result if needed from the appropriate official source or specialist. See the terms of use.

How it works?

Compound interest means you earn interest not just on your original principal, but also on the interest you've already accumulated. Over time, this snowball effect can dramatically grow your savings.

The formula at the core is: A = P × (1 + r/n)^nt, where P is the principal, r the annual rate, n the compounding frequency per year, and t the number of years. Regular monthly contributions (PMT) are added at the end of each compounding period - every month with monthly compounding, once a year with annual compounding - and earn interest from the next period on.

The three modes let you answer the questions people actually ask: How much will I have? (Grow), What do I need to save? (Goal), and Which strategy wins? (Compare).

Frequently asked questions

What is compound interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which is only calculated on the principal), compound interest grows exponentially over time - the longer the period, the more pronounced the effect.

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How does compounding frequency affect growth?

More frequent compounding means slightly higher returns. Daily compounding yields a little more than annual compounding at the same nominal rate, because interest is added to the balance more often, creating a larger base for future interest. The difference becomes more significant at higher rates and over longer periods.

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What is the Rule of 72?

The Rule of 72 is a quick mental calculation: divide 72 by your annual interest rate to estimate how many years it takes for an investment to double. For example, at 6% annual interest, your money doubles in roughly 72 ÷ 6 = 12 years. It's a rough approximation, but remarkably accurate for rates between 2% and 15%.

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Why does starting early matter so much?

Each year you delay means one fewer year of compound growth - but the impact isn't linear. The final years of an investment contribute the most absolute growth because the balance is largest. Waiting just five years to start can cost you more in final value than the first ten years of contributions combined. The 'cost of waiting' insight in this calculator shows you exactly what one year of delay costs you.

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How does inflation affect my real returns?

Inflation erodes purchasing power over time. If your investment returns 7% annually but inflation is 2.5%, your real (inflation-adjusted) return is approximately 4.5%. The calculator's inflation field shows you what your future balance is actually worth in today's money - a much more honest picture of your wealth.

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