Compound Interest Calculator
Project investment growth with compound interest and monthly contributions. See future balance, deposits, and interest earned.
How to use this compound interest calculator
Compound interest is how savings and investments grow when earnings stay invested. The two levers you control are contribution size and time. Rate of return is uncertain; contributions are not. Run a conservative rate so the projection does not become a wish.
Formula
Worked example
$10,000 plus $250 monthly at 7% grows to roughly $62,000 in ten years.
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Frequently asked questions
Is this compound interest calculator free?
Yes. It works instantly in your browser with no signup.
Are the results exact?
Results follow the stated formula, but real-world fees, timing, and rounding can vary.
How does compound interest work?
Interest is earned on both the original principal and on interest already credited. More frequent compounding grows the balance slightly faster.
What is a good rate of return to assume?
Long-run U.S. stock market averages are often cited near 7% after inflation, but that is not guaranteed. Try 5% and 9% as a range.
Should I include monthly contributions?
Yes if you invest on a schedule. Contributions usually dominate growth over long horizons compared with the starting balance.
Is this the same as APY?
APY already includes compounding. If you have an APY, you can enter it as the annual rate with matching compounding frequency.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-20.