Compound Interest Calculator
Project the future value of your savings with compound interest, regular contributions, and adjustable compounding frequency.
Compound interest is interest earned on both your original deposit and on the interest already added to it. It is calculated as A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the compounding periods per year, and t the number of years. $10,000 at 7% for 20 years grows to about $38,697 with no further deposits.
Balance over time
Make compounding work for you
Compound interest is often called the eighth wonder of the world for good reason: the earlier you start and the longer you stay invested, the more of your final balance comes from growth rather than your own contributions. Adjust the starting amount, monthly contribution, rate, and time horizon above to see how each lever changes the outcome.
The single biggest factor is time. A modest monthly contribution left to compound for decades routinely outgrows a much larger sum invested later. Once you know your target, the savings goal calculator can tell you exactly how much to set aside each month.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and on the interest it has already earned. Over time this snowball effect makes your balance grow faster and faster.
How is compound interest calculated?
Each period, your balance is multiplied by (1 + the periodic interest rate), then any new contribution is added. Repeating this over many periods produces exponential growth. This calculator simulates it month by month.
What interest rate should I use?
For a savings account, use its APY (often 4–5%). For long-term stock market investing, many people model around 7% per year after inflation, though real returns vary and are never guaranteed.
How does compounding frequency affect my returns?
The more often interest compounds — daily versus annually — the slightly more you earn, because interest starts earning interest sooner. The difference is small compared to your rate, contributions, and time horizon.
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