CalcArcade.

Compound Interest Calculator

See what a starting amount and regular monthly deposits grow to over time at a given annual rate, with a year-by-year breakdown.

Your numbers

Result

Estimate for information only, not professional advice. Last reviewed .

How we calculate it

With no contributions, the future value is A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the annual rate, n the compounding periods per year and t the years.

With monthly contributions, the calculator converts the compounding schedule into an equivalent monthly rate, (1 + r ÷ n)^(n ÷ 12) − 1, and adds each contribution at the end of its month before the next month compounds.

How to read your result

  • Future value is what your money grows to, including your deposits and the interest on them.
  • Total contributed is what you put in yourself. Interest earned is the growth on top of it.
  • The breakdown bar shows how interest takes over from deposits in later years: that is compounding.
  • The year-by-year table shows the balance at each year end so you can see when growth speeds up.

Common mistakes

  • Treating a return as a promise. Real investments go up and down, so the result is a what-if, not a forecast.
  • Forgetting inflation. A big future number buys less than it does today.
  • Ignoring fees and taxes, which reduce the real return every year.
  • Starting late and counting on a high return to catch up. Time in the market matters more than a slightly higher rate.

Assumptions and limits

  • Assumes a constant rate. Real investment returns vary year to year and are not guaranteed.
  • Results are before taxes and fees, and are not adjusted for inflation.
  • Contributions are assumed to be deposited at the end of each month.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is earned only on the original amount. Compound interest is earned on the original amount plus previously earned interest, so growth accelerates over time.

Does more frequent compounding matter?

Slightly. Moving from annual to monthly compounding at 6% raises the effective yearly rate from 6.00% to about 6.17%. Daily compounding adds a little more. The rate and time matter far more.

How do I include inflation?

Subtract expected inflation from your rate to estimate growth in today’s purchasing power, for example use 3% instead of 6% if you expect 3% inflation.

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Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: Starting amount ($) = 10000; Monthly contribution ($) = 300; Annual interest rate (%) = 6; Years to grow = 20; Compounding = Monthly.

  • Future value $171,714.31
  • Total contributed $82,000.00
  • Interest earned $89,714.31

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.