Calculate compound interest growth over time with customizable principal, rate, frequency, and contributions.
Type the initial investment or deposit amount.
Enter the annual interest rate and compounding frequency.
Set the number of years for the investment to grow.
See the final amount, total interest earned, and growth chart.
This tool projects how a starting balance grows when interest is credited and reinvested at fixed intervals, optionally with regular deposits added along the way. You enter a principal, an annual rate, how often interest compounds (annually, monthly, daily, etc.), a time span, and an optional contribution amount, and it steps through each compounding period applying the rate before returning the ending balance, total contributed, and total interest earned. The most common surprise: raising the compounding frequency while keeping the stated annual rate the same still increases the payout, because interest is credited and starts earning its own interest more often - two runs with the same 'rate' but different frequencies will not match.
A concrete input and expected output from the current implementation.
Input
Principal: $10,000, Annual rate: 6%, Compounding: monthly, Time: 10 years, Contributions: $0
Expected output
Ending balance: $18,193.97 (total interest: $8,193.97)
Monthly compounding over 10 years applies the rate 120 times at 0.5% per period, so the balance grows by a factor of (1 + 0.06/12)^120 = 1.819397, giving 10,000 x 1.819397 = 18,193.97.
The tool divides the annual rate by the number of compounding periods per year and applies that per-period rate repeatedly for the number of periods in the term, equivalent to A = P(1 + r/n)^(nt). It does not apply the stated annual rate once per year regardless of the chosen frequency - changing the frequency changes the number of times growth compounds.
When a periodic contribution is set, it is added once per compounding period and then earns interest for the remaining periods in the term, the same mechanics as a future-value-of-annuity calculation. Contributions made later in the term have less time to compound and add proportionally less to the final balance than earlier ones.
No. The ending balance is a nominal figure in future dollars, not adjusted for purchasing power. If you want a real (inflation-adjusted) figure, subtract an assumed inflation rate yourself, for example by discounting the result using your own estimate of average annual inflation over the term.
The contribution field applies a single recurring amount every period, not a one-time add-on. To model a mid-term lump sum, run the calculator for the period before the deposit, then run it again using that result plus the extra deposit as the new principal for the remaining time.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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