moneycalc

Compound Interest Calculator

See how your investments grow over time with the power of compound interest. Visualize your growth with interactive charts.

Investment Details

$
$
%

S&P 500 historical average: ~10% (7% after inflation)

years

Final Balance

$691,150
Total Contributions$190,000
Total Interest Earned$501,150
Final Balance$691,150

Your money grew 3.6x thanks to compound interest.

Growth Over Time

Contributions Interest

The Power of Compound Interest

Compound interest is interest earned on both your initial principal and previously earned interest. Albert Einstein reportedly called it "the eighth wonder of the world." The key factors are: starting amount, regular contributions, rate of return, and time.

Even small monthly contributions can grow into substantial sums over decades. For example, $500 per month at 7% annual return grows to over $566,000 in 30 years - but only $190,000 of that is your money. The rest is compound interest.

Frequently Asked Questions

What return rate should I use?

The S&P 500 has historically returned about 10% per year before inflation (roughly 7% after inflation). For conservative estimates, use 6-7%. For a diversified portfolio with bonds, 5-6% may be more realistic.

How often is interest compounded?

This calculator assumes monthly compounding, which is standard for most investment accounts. The difference between monthly and daily compounding is minimal for most practical purposes.

Does this account for taxes?

This calculator shows pre-tax growth. In a tax-advantaged account (401k, IRA, Roth IRA), your investments grow tax-free or tax-deferred. In a taxable brokerage account, you'll owe taxes on dividends and capital gains.