Compound Interest Calculator
What a starting amount plus regular monthly contributions could grow to over time.
⚠ This is a projection, not a prediction
The interest rate you enter is an assumption, not a guarantee — real returns vary year to year and can be negative. Use this to compare scenarios, not to plan around one exact outcome.
How this is calculated
Your starting amount compounds monthly at the given annual rate, and your monthly contributions are added to that same compounding growth — interest earns interest, which is what makes it "compound."
Example: $1,000 to start, $100/month, 10 years, 6% annual → about $18,207 from $13,000 contributed — roughly $5,207 in interest.
Why starting early matters more than the amount
- 5 years: $1,000 + $100/month at 6% → about $8,326 (≈$1,326 interest).
- 10 years: same inputs → about $18,207 (≈$5,207 interest).
- 20 years: same inputs → about $49,514 (≈$24,514 interest) — the growth curve steepens over time as interest compounds on more accumulated interest.
Frequently asked questions
Interest is calculated and added to your balance every month (at 1/12th of the annual rate), so next month's interest is calculated on a slightly larger amount than this month's — that repeated small boost is what compounding means.
Yes — it works for anything with a roughly steady average annual return: a savings account, a bond, or an assumed average return for stocks or crypto. Just remember it's your assumption driving the number, not a market guarantee.