Compound Interest Calculator

See exactly how your money grows: enter an initial investment, a monthly contribution and an annual rate, then watch compounding turn steady deposits into serious wealth. Compare compounding frequencies, explore the year-by-year growth chart and schedule below. Everything runs in your browser; no signup, no data leaves your device.

By UpnixTools · Calculator and figures last reviewed September 2026

Investment Details

Monthly contributions are combined and added at each compounding interval, then interest is applied.

Your Projected Growth

Future value
$0
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Total contributions$0
Total interest earned$0
Interest share
0%
Effective APY
0%
Doubling time
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Growth multiple
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Contributions Interest earned

Estimates only, for education — not financial advice. Returns are never guaranteed; actual investment results vary. This projection uses nominal dollars and does not subtract taxes, fees or inflation.

Year-by-Year Breakdown

Cumulative totals: how much you put in, how much interest did the work, and the running balance.

YearContributionsInterestBalance

What is compound interest?

Compound interest is interest earned on both your original money and the interest you have already earned. Each compounding period, your balance grows — and the next period's interest is calculated on that bigger balance. Early on the growth looks slow, but over years the curve bends upward sharply. That is why starting early usually beats waiting, even with smaller deposits.

A = P(1 + r/n)nt

Where A is the final amount, P the initial principal, r the annual rate (as a decimal), n the number of compounding periods per year, and t the number of years. Monthly contributions are added on top: this calculator combines each month's deposit and adds it at every compounding interval before interest is applied.

The Rule of 72

A quick mental shortcut: divide 72 by your annual rate to estimate how many years it takes your money to double. At 7%, that's about 10.3 years; at 9%, about 8 years. Try it above — the "Doubling time" stat updates with your rate.

Tips to maximize compounding

Compound Interest FAQs

How does compound interest work?
You earn interest on your original deposit and on all the interest already added to it. Each period your balance grows, so the next period's interest is calculated on a larger amount. Over time this creates accelerating, snowball-like growth — which is why starting early matters more than chasing a slightly higher rate.
What is a good rate of return?
It depends on the account. US high-yield savings accounts have recently paid around 4–5% a year, while the US stock market has averaged roughly 10% a year over the long run (about 7% after inflation). For planning, many people model a conservative 6–8% for invested money and 4–5% for cash savings. This calculator defaults to 7% as a middle ground.
Daily vs monthly compounding — does it matter?
Barely. On $10,000 at 7% for 10 years, monthly compounding gives about $20,097 while daily compounding gives about $20,136 — a difference of less than $40. Your rate, your contributions and your time horizon matter far more than the compounding frequency.
How much will $10,000 grow in 10 years at 7%?
About $20,097 with monthly compounding and no extra contributions — roughly doubling your money. That matches the Rule of 72, which predicts doubling in about 10.3 years at 7%. Add $500 a month and the same scenario grows to roughly $107,000.
Is compound interest taxed?
In the US, yes — in a regular taxable account. Bank interest is taxed as ordinary income each year, and investment gains are taxed when you sell (usually at lower long-term capital gains rates if held over a year). Inside a 401(k) or traditional IRA, growth is tax-deferred; inside a Roth IRA it can be tax-free in retirement.
Does this calculator include inflation?
No — it projects nominal dollars, the number you would actually see on a statement. US inflation has averaged around 2–3% a year over the long term, so for a rough "real" purchasing-power estimate, subtract about 3 percentage points from your assumed return. A 7% nominal return is roughly a 4% real return.

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