Compound Interest Calculator
See how your money grows with compounding over time.
Your Inputs
Future balance
Contributed
Interest earned
How to Use This Calculator
2. Add your monthly contribution.
3. Set your expected annual return and time horizon with the sliders.
4. Choose how often interest compounds.
Results and the growth chart update instantly.
Calculation Method
FV = P(1 + r/n)^(nt) + PMT × [((1 + rm)^m − 1) / rm]
P = principal, PMT = monthly contribution, r = annual rate, n = compounds/year, rm = r/12, m = months, t = years. Returns are user-assumed and not guaranteed.
Source: Standard compound interest / annuity future-value formula.
Conservative
$10k + $300/mo · 5% · 25 yr
≈ $213,000
Balanced
$10k + $500/mo · 8% · 30 yr
≈ $745,000
Aggressive
$10k + $800/mo · 10% · 35 yr
≈ $3.0M
Frequently Asked Questions
What is compound interest?
Interest earned on both your principal and previously earned interest, so your balance grows at an accelerating rate over time.
How does compounding frequency change the result?
More frequent compounding (monthly vs annually) gives a slightly higher balance; the gap widens with longer horizons and higher rates.
What annual return should I assume?
Historically the S&P 500 returned roughly 10% nominal (about 7% after inflation). Many investors model 6–8% to stay conservative. Returns are never guaranteed.
Does this include inflation or taxes?
No. It shows nominal growth. Subtract your assumed inflation rate for real purchasing power; taxes depend on your account type.
Is the calculator free?
Yes — completely free, no signup, no limits.
Related Calculators
ROI Calculator
Measure total and annualized return on any investment.
Open →CAGR Calculator
Compute the compound annual growth rate of an asset.
Open →Dollar Cost Averaging Calculator
Compare dollar-cost averaging vs lump-sum investing.
Open →Dividend Reinvestment (DRIP) Calculator
Project wealth from reinvested dividends.
Open →Related Guides
Last updated: May 24, 2026