Compound Interest
Compound Interest Calculator
Plug in a starting balance, monthly contribution, expected return, and time horizon. See what compounding does.
Final balance
$618,102
You contributed
$181,000
Investment growth
$437,102
FAQ
What is compound interest?
Compound interest is when the returns you earn start generating their own returns. Each year your investment grows by a percentage of a now-larger balance, accelerating over time.
What's a realistic annual return for stocks?
Historically the S&P 500 has averaged around 10% nominal (about 7% after inflation). Individual years vary wildly — assuming 6–8% in long-term projections is reasonable and conservative.
Should I include inflation?
Yes — subtract roughly 2–3% from your assumed return to see real (inflation-adjusted) purchasing power, which is what matters.