Compound Interest Calculator
FinanceCalculate how your investment grows over time with compound interest, including optional regular contributions on top of your initial investment.
Future Value
Total value at end of period, including your initial investment and every contribution
Interest Earned
$20,713.58
Total interest earned, excluding your own principal and contributions
Total Contributions
$24,000.00
The sum of every contribution you make over the full time period, not counting the initial investment
Return on Initial Investment
447.1%
Future value as a percentage return on your initial investment alone, not counting contributions
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Finance calculators
This calculator finds the future value of an investment growing with compound interest, including optional regular contributions added on top of your initial investment. Enter your initial investment, how much you plan to contribute each period, your annual interest rate, the time period, and your compounding frequency.
The Contribution per Period field is added once per compounding period, so if you choose Monthly compounding, it's added monthly, if you choose Annually, it's added once a year, and so on. Leave it at zero to see growth from your initial investment alone, with no ongoing contributions.
The exact formula, why compounding frequency and contribution timing both matter, and answers to common compound interest questions are below.
The compound interest formula, with contributions
Future value equals your principal times (1 plus the periodic rate) raised to the number of periods, plus the value of your contributions compounding the same way. Each contribution earns interest for the periods remaining after it's made, so an early contribution ends up worth more than a later one of the same size. For a 10,000 dollar initial investment plus 200 dollars contributed monthly, at 7 percent annual interest compounded monthly for 10 years, the future value comes to 54,713.58 dollars: 24,000 dollars from your own contributions, and 20,713.58 dollars in interest earned.
Why compounding frequency changes the result
More frequent compounding means interest starts earning its own interest sooner, which produces a slightly higher future value at the same stated annual rate. The difference is usually modest at typical savings rates, but it compounds (in the literal sense) over a long time period, so it's worth matching whatever frequency your actual account or investment uses rather than assuming.
Lump sum vs. regular contributions
Growing an investment through a single lump sum and growing it through regular contributions are both valid strategies, and this calculator handles either one, or a combination of both, in the same result. If you want a version built specifically around regular monthly contributions to a taxable brokerage account, see the Investment Calculator. For a simpler, deposit-focused version aimed at a savings account specifically, see the Savings Calculator.
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, it grows exponentially over time.
How often should interest compound?
The more frequently interest compounds, the faster your money grows. Daily compounding produces slightly more than monthly, which produces more than annual, though the difference narrows at lower interest rates.
What is the Rule of 72?
The Rule of 72 is a quick estimate: divide 72 by your annual interest rate to find approximately how many years it takes your investment to double. At 7% annual interest, your money doubles roughly every 10.3 years.
Does this calculator include regular contributions?
Yes. Set the Contribution per Period field to the amount you plan to add each compounding period. Leave it at zero for a lump-sum-only calculation.
When are contributions added during each period?
This calculator assumes contributions are added at the end of each compounding period, the standard convention used by most real compound interest calculators, meaning the contribution made in the final period doesn't have time to earn interest before the calculation ends.
Why is Total Interest less than Future Value minus my initial investment?
Total Interest specifically excludes your own money, both your initial investment and every contribution you made, so it only counts interest actually earned. Future Value minus your initial investment would still include your contributed principal, not just the interest.
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