Compound Interest Calculator
See how savings or investments grow with compound interest over time.
Final balance
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Total contributed
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Interest earned
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Hover the chart to read the balance at a given year. The dashed line is total contributed (no interest); the gap to the solid line is interest earned.
Estimates from standard formulas — not financial advice. They don't capture every fee, tax, or rate change; check important decisions with a lender, adviser, or accountant. Full disclaimer.
About this tool
See how a starting amount grows when interest compounds, with an optional regular monthly contribution added along the way. The chart separates the money you put in from the interest it earned, so you can see the gap widen over time.
What compounding means. Interest is added to the balance, and then the next period's interest is calculated on that larger balance. Growth therefore accelerates: the curve is not a straight line. The amortization guide shows the same mechanism running in reverse on a loan.
How it's calculated. The starting amount grows by the standard compound formula A = P(1 + r/n)nt, where r is the annual rate, n is the number of compounding periods per year, and t is the number of years. Monthly contributions are added with a future-value-of-a-series calculation using the same frequency, then the two results are combined.
Worked example. $5,000 at 7% for 10 years, compounded monthly, with no contributions, grows to about $10,048 — roughly doubling. Add $200/month and the final balance is about $44,700, of which $29,000 is money you contributed and about $15,700 is interest.
Does compounding frequency matter? Less than people expect at everyday rates. $10,000 at 5% for 20 years comes to $27,126 compounded monthly versus $27,181 compounded daily — a difference of $55 over two decades. The gap widens with higher rates and longer horizons, but the rate and the time invested dominate.
What this leaves out. It assumes a single constant rate of return. Real investments fluctuate, and a 7% average is not 7% every year — a bad year early on hurts more than the same year late. It also ignores inflation (which erodes what the final balance can buy), taxes on gains, and fund fees. It's a planning estimate, not financial advice.
For retirement-specific planning use the retirement calculator; to compare paying down debt against investing spare cash, put the loan into the loan calculator and the cash into this one.
Frequently asked questions
- What formula is used?
- Compound interest on the starting amount — A = P(1 + r/n)^(nt) — plus a future-value-of-a-series calculation for the recurring monthly contributions, both using the compounding frequency you select.
- Does compounding frequency make a big difference?
- Usually a small one. At everyday rates the difference between monthly and daily compounding is a fraction of a percent of the final balance. It grows with higher rates and longer time periods.
- What if I don't add monthly contributions?
- Leave that field at 0 or empty to see pure compound growth on the starting amount alone.
- Is the interest rate before or after inflation?
- It's a nominal rate — before inflation. To reason in today's money, enter a lower "real" rate (roughly the nominal rate minus expected inflation).
- Why doesn't my real investment track this line?
- This assumes a fixed rate every year. Markets vary, and the order of good and bad years matters: a loss early in the period has a larger effect than the same loss near the end.
- Does it account for tax or fees?
- No. Taxes on interest or capital gains, and any account or fund fees, would reduce the real outcome. Subtract an estimate of those from the rate if you want a more conservative figure.