Compound Interest Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
auto_graph Snowball effect
Interest earned in earlier periods earns its own interest, accelerating growth over time.
schedule Time matters most
Doubling your time horizon usually grows the result more than doubling your contribution.
percent Rate sensitivity
A 1-point rate change over 30 years can swing the final balance by 30% or more.
savings Regular deposits
Steady monthly contributions outperform a single lump sum at the end.
Quick reference
Future value of a one-time $10,000 deposit, compounded monthly, with no extra contributions:
| Annual rate | After 10 years | After 20 years | After 30 years |
|---|---|---|---|
| 4% | $14,908 | $22,226 | $33,135 |
| 6% | $18,194 | $33,102 | $60,226 |
| 8% | $22,196 | $49,268 | $109,357 |
savings Plan with confidence
Finance decisions get a lot easier when you can see the full picture. Enter your numbers above to see total payments, interest paid, and the long-term cost of every choice — so you can compare options side by side before signing anything.
percent How the math works
We use the standard amortization, compound-interest and present-value formulas published by the Consumer Financial Protection Bureau and the Federal Reserve. The methodology block below shows every variable and rounding step we apply, so the answer is never a black box.
shield_lock Your data stays private
Every calculation happens in your browser with JavaScript — your income, balances, and loan numbers are never sent to our servers, logged, or shared. Close the tab and the inputs vanish. No sign-up, no tracking pixels on the form, no spreadsheet emailed to you later.
lightbulb Pro tip
Save the URL after you calculate — your inputs aren't stored, so write down the headline number plus the breakdown. Then come back and edit one variable at a time (down payment, rate, term) to see exactly which lever moves your monthly figure the most. That's where the real planning happens.
Interpretation guide
The more often interest compounds, the higher the effective return — though the jump from monthly to daily is small. Effective annual rate (EAR) on a 6% nominal rate:
| Compounding frequency | Effective annual rate (EAR) |
|---|---|
| Annually | 6.00% |
| Semi-annually | 6.09% |
| Quarterly | 6.14% |
| Monthly | 6.17% |
| Daily | 6.18% |
The biggest drivers of your result are always the rate and the time invested — not the compounding frequency.
lightbulb Example — $10,000 at 5% compounded monthly for 10 years
Result: Future value = $16,470.09 ($6,470.09 interest).
What this means: Compounding monthly beats annual compounding; the more often interest compounds, the more you earn.
Formula & methodology
Formula: A = P(1 + r/n)^(nt) • with deposits: FV = P(1+r/n)^(nt) + PMT × [((1+r/n)^(nt) − 1) ÷ (r/n)]
Compound interest pays interest on your original deposit and on the interest already earned, so a balance grows exponentially rather than in a straight line. The standard formula is:
A = P(1 + r/n)nt
- A — final amount (future value)
- P — principal (starting deposit)
- r — annual interest rate as a decimal (6% = 0.06)
- n — compounding periods per year (monthly = 12)
- t — number of years
When you add regular contributions (PMT), the calculator also sums the future value of every deposit. The effective annual rate (EAR) — the true yearly return once compounding is counted — is (1 + r/n)n − 1. A quick mental check is the Rule of 72: divide 72 by the rate to estimate the years it takes your money to double (72 ÷ 6% ≈ 12 years).
Authoritative source: U.S. Securities and Exchange Commission