Savings & growth
Compound Interest Calculator
Small, regular contributions compound into large numbers over long enough time. See what yours could look like.
Interactive tool
Compound Interest Calculator
Investment growth with monthly contributions. Final balance, contributions vs interest earned, and a year-by-year snapshot.
Historical S&P 500 average: ~10% nominal / ~7% real after inflation (FRED long-run average). Past returns don't guarantee future results.
Final balance after 30 years
$691,150
- Total contributions
- Starting balance + monthly contributions over 30 years
- $190,000
- Total interest earned
- Final balance minus total contributions
- $501,150
- Interest as % of final balance
- How much of the final number is compounding (not deposits)
- 72.5%
Contributions vs growth
Frequently asked
Where should compounding money actually sit?
That depends on the time horizon and how much risk you can stomach. Cash you'll need within a couple of years belongs in an FDIC-insured high-yield savings account or CD, not the market. Longer horizons can tolerate market volatility for a shot at a higher average return. This calculator lets you test a rate assumption either way — it doesn't tell you which account to pick.
Why does compounding frequency (monthly vs. annually) matter?
More frequent compounding means interest starts earning its own interest sooner, so monthly compounding produces a slightly higher final balance than annual compounding at the same stated rate. The difference is usually small compared to the rate itself and the time horizon — don't let it distract from the bigger levers (contribution amount and time).
Is 7% a realistic long-term return assumption?
It's the commonly cited historical real (after-inflation) average for the S&P 500 over long periods, per FRED long-run data. It's a reasonable planning assumption for a diversified, long-horizon portfolio — not a guarantee. Markets are volatile year to year; use a range of assumptions rather than anchoring on one number.