Compound Interest Calculator
Estimate how savings or investments grow over time with compound interest, optional monthly contributions and adjustable compounding frequency.
Examples
Optional extras
Year-by-year breakdown
Export options
How it works
Enter a starting amount, a contribution per selected period, nominal APR and duration. The calculator uses the same formula as the Investor.gov calculator at your selected annual, semiannual, quarterly, monthly or daily frequency, with end-of-period contributions as the labeled default.
APR and EAR stay visible, while the stacked bars retain the initial-principal, contribution and interest split. The inflation switch converts balances into today's purchasing power; CSV, print and result-card exports stay in your browser.
FAQ
How is compound interest calculated?
It uses the same formula as the Investor.gov calculator (at the selected frequency). The nominal APR is divided by 1, 2, 4, 12 or 365 periods per year, and the calculator applies interest and one contribution in each selected period.
When are contributions added?
Choose beginning or end of each compounding period. End of period is the default: interest is credited first, then the contribution is added. Beginning-of-period contributions earn interest during that period. The contribution amount is per selected period, not always per month.
What are APR and EAR?
APR is the nominal annual rate you enter. EAR is the effective annual rate after compounding: EAR = (1 + APR / n)^n − 1. More frequent compounding makes EAR higher when APR is positive.
Can I see the year-by-year growth?
Yes. A stacked bar chart splits every year’s balance into initial principal, contributions and interest, and the year-by-year table shows the starting balance, money added, interest earned and ending balance for each year.
What is the doubling time and the Rule of 72?
The Rule of 72 is a quick mental estimate: divide 72 by the nominal APR to estimate doubling time. The exact figure uses the selected compounding frequency, so it changes when you switch between annual, semiannual, quarterly, monthly and daily compounding.
How does the inflation adjustment work?
Turn on “Adjust for inflation” and enter an expected inflation rate. The calculator then shows the real purchasing power of every balance in today’s dollars — as an extra column in the table, a dashed line on the chart and a “In today’s money” stat.
Can I download or print the results?
Yes. “Download CSV” saves the year-by-year table as a spreadsheet file, generated entirely in your browser — nothing is uploaded. “Print” produces a clean document with the chart and full table, and “Share as image” creates a summary card.
Is this financial advice?
No. It is an estimate for planning only and does not account for taxes or fees. Real investment returns vary year to year.
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