Compound Interest Calculator with Growth Chart
See how your savings grow with compound interest and regular contributions. Compare monthly, quarterly and annual compounding with a year-by-year breakdown and chart.
Your savings plan
Historically, broad stock market indices have averaged roughly 7% after inflation.
Balance after your time horizon
$302,370
57% of that total is interest you did not deposit
- You contribute
- $130,000
- Interest earned
- $172,370
- Final balance
- $302,370
How compound interest works
With simple interest you earn a fixed amount on your original deposit forever. With compound interest, each payment of interest joins your balance — and then earns interest of its own. That feedback loop is why the chart above curves upward instead of climbing in a straight line.
The standard formula is A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods per year, and t the number of years. This calculator steps through month by month instead, so regular contributions are handled correctly rather than approximated.
Time matters more than rate
This is the least intuitive part of compounding. Consider 500 per month at 7%:
- After 10 years: about 86,000, of which 26,000 is interest
- After 20 years: about 260,000, of which 140,000 is interest
- After 30 years: about 610,000, of which 430,000 is interest
Contributions tripled between the first and third row, but interest grew more than sixteen-fold. Most of compounding's work happens in the final third of the timeline, which is precisely why starting earlier beats contributing more later.
Reading the chart
The grey portion of each bar is money you deposited; the coloured portion is interest. The year those two areas cross is the point where your money is earning more than you are adding to it — a genuinely useful milestone to plan toward.
Be honest about the rate you enter
Results are nominal and ignore inflation, tax and fees. If you want to think in today's money, subtract expected inflation from your return: a 10% nominal return with 3% inflation is 7% real. A 1% annual management fee compounds against you in exactly the same way it compounds for you, so subtract that too.
A note on when contributions land
This calculator adds your monthly contribution at the start of each month, so it earns interest during that month. Some calculators add it at the end instead. The difference is small — well under 1% over a long horizon — but it explains why two tools can disagree slightly on the same inputs.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original deposit and on the interest already added to it. Because each period's interest joins the balance that earns the next period's interest, growth accelerates over time rather than staying flat like simple interest.
How much difference does compounding frequency make?
Less than most people expect. On 10,000 at 7% for 10 years, annual compounding gives about 19,672 and monthly gives about 20,097 — a difference near 2%. Your contribution rate and the number of years matter far more than how often interest is applied.
What is the Rule of 72?
Divide 72 by your annual interest rate to estimate the years needed to double your money. At 8%, that is roughly 9 years. It is a mental shortcut rather than an exact formula, but it stays within about a year of the true figure for rates between 5% and 12%.
Does this account for inflation or tax?
No — the results are nominal figures before inflation and tax. To think in today's purchasing power, subtract your expected inflation rate from the return rate. Entering 7% instead of 10% is a common way to approximate a real, inflation-adjusted return.
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Last updated August 22, 2026