Compound Interest Calculator

Plug in an initial investment, monthly or yearly contributions, an expected annual return, and any one-off deposits. See your future balance, the interest you earn, and how a small change in time or contributions changes everything.

• Currency: Currency

• Currency Aria: Select currency

• Initial: Initial investment

• Contribution: Regular contribution

• Frequency: Frequency

• Frequency Aria: Contribution frequency

• Monthly: Monthly

• Yearly: Yearly

• Contrib Growth: Contribution growth

• Contrib Growth Hint: Increase your regular contribution by this percentage every year or month. Useful to keep up with salary raises or inflation.

• Contrib Growth Freq: Increase frequency

• Contrib Growth Freq Aria: Frequency at which the contribution is increased

• Contrib Growth Off: Set a percentage to apply the increase.

• Contrib Growth Freq Hint: Controls how often the percentage is applied to your contribution.

• Annual Rate: Expected annual return

• Years: Investment period

• Years Unit: yr

• Compounding: Compounding

• Compounding Aria: Compounding frequency

• C Monthly: Monthly

• C Quarterly: Quarterly

• C Yearly: Yearly

• Extras: Extra deposits

• Extras Hint: One-off contributions like a year-end bonus, holiday money, an inheritance or expected extra income. Add a date.

• Add Extra: Add deposit

• No Extras: No extra deposits added.

• Extra Label: Description

• Extra Label Placeholder: Year-end bonus, vacation money, ...

• Extra Amount: Amount

• Extra Date: Date

• Remove Extra: Remove deposit

• Duplicate Extra: Duplicate deposit

• Repeat Yearly: Repeat yearly

• Repeat For: for

• Repeat Years Aria: Number of additional years to repeat

• Reset All: Reset

• Advanced Title: Advanced (optional)

• Advanced Hint: Stress-test your projection with a return range, account for inflation, or estimate what you keep after capital gains tax. All off by default.

• Variation: Return variation (±)

• Variation Hint: Show a pessimistic and optimistic projection by varying the annual return up and down.

• Inflation: Annual inflation

• Inflation Hint: Discount the future balance back to today’s purchasing power.

• Inflation Active Hint: Real balance shown in today’s money below.

• Tax: Capital gains tax

• Tax Hint: Flat tax applied to your interest at the end (e.g. 30% in Belgium on bonds).

• Tax Active Hint: After-tax balance shown below. Contributions are not taxed again.

• Range Label: Range (low – high)

• Real Balance: In today’s money

• After Tax: After tax

• Final Balance: Final balance

• Total Contributed: Total invested

• Total Interest: Compound interest earned

• Legend Contrib: Contributions

• Legend Interest: Interest

• Year: Year

• Compare Years Title: Compare investment periods

• Compare Years Hint: Same contributions and rate, different time horizons. Time is the most powerful lever in compound growth.

• Compare Contrib Title: Compare contribution amounts

• Compare Contrib Hint: Same period and rate, different amounts you put in each month. See what doubling your contribution actually does.

• Col Years: Period

• Col Monthly: Monthly contribution

• Col Yearly: Yearly contribution

• Col Contributed: Total invested

• Col Interest: Interest earned

• Col Balance: Final balance

• Current: current

• About Title: How compound interest works

About

• Compound interest is interest you earn on your interest. Every period, the previous interest is added to your principal, so the next period's interest is calculated on a slightly larger base. Over decades, that small effect snowballs into the bulk of your final balance.

• Three things move the needle: how much you start with, how much you add each month or year, and how long you stay invested. The annual rate matters too, but time is almost always the strongest lever. Doubling the years you stay invested usually does more than doubling the amount you contribute.

• This calculator uses a standard compound interest formula and supports monthly, quarterly or yearly compounding. One-off deposits with a date are added in the month they fall in, so a year-end bonus or vacation money is reflected exactly when it lands in your account.

• Formula Label: Compound interest formula

• Formula Legend: A = final amount, P = principal, r = annual rate (decimal), n = compounds per year, t = years, PMT = recurring contribution.

• Faq Title: Frequently asked questions

Faq

What is compound interest, in plain terms?

It is the interest you earn on money that already includes earlier interest. Instead of only your original deposit earning a return, your returns also start earning their own returns. The longer you let it run, the more dramatic the effect.

What is a realistic annual return to use?

It depends on what you invest in. Cash savings accounts in Europe typically return 1–3%, broad stock-market index funds have historically averaged around 6–8% per year over the long run after inflation depending on the period, and individual stocks vary wildly. Use a conservative number if you want a safer estimate.

How is monthly compounding different from yearly?

With monthly compounding, interest is added to your balance every month, so next month's interest is calculated on a slightly bigger amount. Yearly compounding only does this once a year. The difference is small at low rates but grows with longer periods and higher returns.

Should I contribute monthly or yearly?

Monthly contributions earn interest a little earlier, so they end up slightly ahead of the same yearly amount. The difference is usually a few percent over decades. Whichever fits your cash flow and discipline best is the right choice.

Are taxes and inflation included?

Yes, both are optional inputs in the Advanced section, off by default. Add an inflation rate to see your final balance in today’s money. Add a capital gains tax rate to see what you keep after tax (only your interest is taxed, your contributions come back untaxed). You can also add a return variation to stress-test the projection with an optimistic and pessimistic scenario. Tax rules depend entirely on your country and account type, so use a number that fits your situation.

Is my data sent anywhere?

No. Everything runs locally in your browser. Nothing is uploaded, stored or shared. Refresh the page and your inputs are gone.

• Cta Label: Want a financial tool built around your numbers?

• Cta Title: Want a calculator like this, or the full platform around it, built for you and ready to use?

• Cta Button: Get in touch

• Disclaimer: For educational purposes only. This is not financial advice. Real returns vary, are not guaranteed, and depend on the investments you choose, fees, taxes and inflation.

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