Compound Interest Calculator
Use this free compound interest calculator to see how your savings or investments could grow over time. Add a starting amount, set a monthly or yearly contribution, choose your expected return and time horizon, and instantly see your projected future balance — along with how much of it is your own money versus compounded growth.
It even lets you adjust for compounding frequency, inflation and tax on gains, so the result reflects something close to the real world. No account, no sign-up, no spreadsheet required.
▶ Adjust for inflation & tax
▸ Show year-by-year breakdown
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Estimates are for illustration and education only — not investment advice. Real returns vary and are not guaranteed.
The compound interest formula
Compounding means earning returns on your returns. The full formula combines a lump sum growing on its own with the accumulated value of every regular contribution.
How to use the compound interest calculator
Four short steps. Change any field and the future balance, chart and yearly breakdown update instantly.
Enter your starting amount
This is your initial deposit, or principal. Starting from zero is fine — the contributions do the work.
Add a regular contribution
Choose how much you'll add each month or year. Consistency matters more than the size of any single deposit.
Set your rate and time horizon
Pick an expected annual return and drag the slider to the number of years you plan to stay invested.
Fine-tune for the real world
Open the advanced options to adjust compounding frequency, inflation and tax on gains for a realistic estimate.
What this calculator tells you
Compound interest is the process of earning returns not only on the money you originally invest, but also on the returns that money has already generated. Over months and years, those returns begin to generate returns of their own — and your balance grows along a curve that gets steeper with time. This calculator turns that idea into concrete numbers for your plan.
Future balance vs. money invested
The headline figure is your projected future balance. Just below it, the calculator splits that total into two parts: total invested (the money you put in yourself) and interest earned (the growth compounding produced for you). Over long horizons, the interest portion often grows far larger than everything you contributed — a clear illustration of why time in the market is so powerful.
Why compounding frequency matters
How often interest is added back to your balance affects the result. Monthly compounding generally produces a slightly higher total than annual compounding, because your gains start earning their own gains sooner. For most ETF and index-fund investors, monthly is a sensible, realistic default.
Adjusting for inflation and tax
A balance that looks impressive in 30 years will buy less than the same number does today, because of inflation. Enabling the inflation field shows your result in today's purchasing power. Likewise, the tax on gains field gives you a rough sense of what you might keep after tax. Both are simplifications — your actual tax treatment depends on your account type and country — but they make the projection more honest.
Who it's for
This tool is built for everyday savers and long-term investors: anyone opening their first index fund, building a retirement pot, saving for a child, or simply curious whether small monthly contributions are worth it. You don't need any financial background — just a few numbers and a couple of minutes.
Want the deeper story behind the math? Read our article on why compound interest beats timing the market, or jump back to the full explainer on the homepage.