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Compound interest calculator

Set your own rate and monthly contribution. Explore a projection, with the assumptions clearly shown.

Your numbers

Example values are filled in. Replace them with your own.

Changes labels only. Amounts are not converted.

Your assumed nominal annual rate; calculated monthly.

12 months = 1 year. Maximum 600 months.

Your numbers stay in this tab.

EXAMPLE ESTIMATE

Your estimate

Enter your values and select Calculate.

Estimates use your assumptions. Calculations use unrounded values; displayed figures are rounded.

HOW IT WORKS

A useful estimate starts with clear inputs.

  1. Step 1

    Enter your starting amount and a regular monthly contribution.

  2. Step 2

    Choose an assumed annual rate and duration. Try several rates to explore different outcomes.

  3. Step 3

    Read the projected balance, total contributions and growth, then download the monthly projection.

Worked example

With 1,000 initially, 100 added monthly and a 0% rate, the balance after 12 months is 2,200.

Calculation assumptions and limits

A constant nominal annual rate divided by 12, monthly compounding and equal contributions at the end of each month. Negative rates model a steady decline. Actual investment returns vary; taxes, fees and inflation are excluded. A projection is not a guaranteed return.

Can I use this with my local currency?

Yes. All inputs in one calculation must use the same currency. The currency selector changes number formatting and labels; it does not look up exchange rates or convert your amounts. Local loan rules and products may calculate costs differently.

Are my numbers saved?

No. Your inputs and results stay in this page’s memory. Reloading or leaving clears them. Download the CSV or print the result if you want a copy.

Learn more: Investor.gov: compound interest calculator. WORDMIO calculates locally using the assumptions above.

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Explore how time and contributions affect a balance

Model a starting amount, recurring monthly contributions and a rate you choose. The result separates money contributed from projected growth so you can see what drives the final balance.

Try more than one rate and time period. This is a mathematical projection with a fixed assumption, not a forecast of market returns or a recommendation for an investment.

Free to use. No sign-up required.

How to use this tool

  1. Enter the starting amount and planned monthly contribution.
  2. Choose an annual rate and a time period in months.
  3. Calculate, then compare contributions with projected growth.

A practical example

Starting with 1,000 and adding 100 each month for 12 months at 0% produces 2,200. At nonzero rates, the model applies monthly interest before adding that month’s contribution.

Before you finish

The rate is an assumption, not a promised investment return. Taxes, fees and inflation are excluded; a currency selection does not convert amounts.

Frequently asked questions

When are contributions added?

The model adds regular contributions at the end of each month, after applying that month's interest.

What compounding rate does the calculator use?

It divides the nominal annual rate by 12 and compounds monthly. An effective annual yield is a different input and should not be treated as the same rate.

Are taxes, fees and inflation included?

No. The projection excludes taxes, fees and inflation. Actual returns can change over time and may be negative.