Compound Interest Calculator
See how your money grows over time.
Final balance
$126,126.13
- Total invested
- $70,000.00
- Interest earned
- $56,126.13
- Effective monthly rate
- 0.8%
- Period
- 120 months
How it works
Compound interest is interest calculated on the initial principal plus all accumulated interest from previous periods — "interest on interest". It is the main driver of long-term investment growth.
Formula:
FV = P × (1 + i)ⁿ + PMT × [((1 + i)ⁿ − 1) / i]
FV = future value, P = principal, i = rate per period, n = number of periods, PMT = periodic deposit.
Practical examples
$10,000 at 1% per month for 5 years
With no deposits, the future value is ~$18,167. In 10 years it reaches ~$32,900.
$1,000 + $500/mo at 0.8%/mo for 10 years
Total deposited: $61,000. Final balance ~$101,500. $40,500 came from interest alone.
Power of time
Starting at 25 with $300/mo beats starting at 40 with $700/mo over the same end age.
Frequently asked questions
Simple vs compound interest — what's the difference?
Simple interest only accrues on the initial principal. Compound interest adds previous interest to the base, so the balance grows exponentially.
How do I convert a yearly rate to monthly?
i_monthly = (1 + i_yearly)^(1/12) − 1. Example: 12%/yr equals 0.9489%/mo, not 1%/mo.
Are deposits at the beginning or end of the period?
This calculator assumes end-of-period deposits (ordinary annuity).
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⚠️ Disclaimer
This calculator is for educational and informational purposes only. Results are estimates based on public formulas and may contain inaccuracies or be outdated. We are not accountants, lawyers, doctors, or financial advisors — for any important decision (tax filings, contracts, diagnoses, financial planning), always consult a qualified professional. calculadora.work assumes no liability for decisions made based on the content of this site.