Compound Interest

Watch your money multiply

Compounding is when your returns earn their own returns. Enter your numbers below to see what time and consistency actually do to a portfolio.

$
$
% / yr
years
—
total value after — years
Total Contributed
—
your money in
Interest Earned
—
the market's contribution
Return Multiple
—
× your money
Growth Over Time
Year-by-Year Milestones

Put compounding to work

The earlier you start, the more dramatic the results. These platforms make it easy to invest consistently with low fees.

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For educational purposes only. Not financial advice. Returns are not guaranteed.

Compound interest is the reason small amounts invested early can grow into life-changing sums. Most people understand the concept but underestimate how powerful it is in practice. The math is straightforward: your returns generate their own returns, and that cycle repeats for as long as your money stays invested.

The two variables that matter most are time and consistency. A higher interest rate helps, but starting early and contributing regularly will outperform a great rate started late almost every time. This calculator lets you model exactly how those variables interact so you can see the impact of your decisions before you make them.

Common Questions

What is compound interest?
Compound interest means you earn returns not just on your original investment but on the returns themselves. Over time this creates exponential growth. The longer your money compounds, the more dramatic the effect becomes.
How often does interest compound?
It depends on the account or investment. Savings accounts often compound daily or monthly. Investment accounts that track index funds compound effectively every time the market moves. The more frequently interest compounds, the faster your balance grows.
Why does starting early matter so much?
Because compounding is exponential. Someone who invests $5,000 a year from age 25 to 35 and then stops will often end up with more money at retirement than someone who invests $5,000 a year from age 35 to 65. Time in the market is more valuable than the amount invested.
What is a realistic rate of return to use?
The S&P 500 has historically returned around 10% annually before inflation, or roughly 7% after inflation. Most financial planners use 6-7% as a conservative long term estimate. Using a lower number gives you a more realistic floor for planning purposes.