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Investing & Retirement

Compound Interest Calculator

See how a starting amount and steady monthly deposits snowball over time. Compound interest is the reason small, consistent saving beats a big deposit made too late.

Your numbers

Adjust anything — the projection recalculates instantly in your browser.

years
%

Projected balance

After 25 years

$271,649

You put in $95,000 and earned $176,649 in growth.

Total contributions

$95,000

Interest / growth

$176,649

Final balance

$271,649

Assumes a constant average annual return, which real markets never deliver year to year. A projection, not a guarantee.

The eighth wonder of the world

Compound interest means your money earns money, and then that money earns money too. The longer it runs, the more dramatic the effect. The chart above makes it visible: the grey line is what you put in, and the green area is what compounding added on top.

Time beats timing

Because growth compounds, when you start matters more than how much you start with. A modest deposit left to grow for 30 years often ends up larger than a bigger deposit that only had 15 years to work.

Example

Start with $5,000, add $300 a month, and earn 7% a year. After 25 years you'd have put in about $95,000 — but the balance would be roughly $260,000. The extra ~$165,000 is compounding.

Put it to work

Turn a target into a plan with the savings goal calculator, model a portfolio with the investment calculator, or estimate your nest egg with the retirement calculator. For a quick doubling estimate, try the Rule of 72.

Related calculators

Investment CalculatorProject the future value of an investment with regular contributions.Retirement CalculatorAre you on track? Project your nest egg to retirement age.Savings Goal CalculatorHow much to set aside each month to hit a savings goal by a date.Rule of 72 CalculatorRoughly how many years it takes your money to double.

Frequently asked questions

What is compound interest?
Compound interest is interest earned on both your original money and the interest it has already earned. Over time the growth accelerates, because each period’s interest is calculated on a larger balance. It’s the engine behind long-term investing.
How does compounding frequency affect growth?
More frequent compounding (monthly vs. annually) earns slightly more, because interest starts earning interest sooner. The difference is modest compared with the rate and time horizon, but it’s real — switch the frequency above to compare.
What return rate should I use?
For a high-yield savings account, use its current APY. For a diversified stock-market portfolio, many people model a long-run average of about 6%–7% after inflation. Lower assumptions are safer for planning.
Why do contributions matter so much?
Early, consistent contributions have the longest time to compound. The chart shows contributions (grey) versus total balance (green) — the widening gap is pure growth working for you.