Compound Interest Calculator

Estimate how an initial deposit and monthly contributions could grow at a fixed annual rate. Compare deposits with interest earned in the growth chart and year-by-year breakdown.

Investment Details

Initial Investment ($)

Monthly Contribution ($)

Added at the beginning of each month. Enter 0 for no monthly additions.

Annual Interest Rate (%)

Annual rate before compounding, not APY.

Investment Period (years)Additional months

240 months total (maximum 100 years).

Compounding Frequency

How often interest is added to the balance. Contributions remain monthly.

Results

Final Amount

$345741.64

Total Contributions

$130000.00

Total Interest Earned

$215741.64

Interest as % of Total

62.4%

Contributions ($130000.00)Interest ($215741.64)

Balance over time

— End Balance┄ Total Contributions

The solid line shows the balance; the dashed line shows deposits. Exact values are in the table below.

A = P(1+i)^m + PMT × (1+i) × ((1+i)^m − 1) / i

i = 8% / 12, m = 240, P = $10000.00, PMT = $500.00

Total Contributions = $10000.00 + $500.00 × 240 = $130000.00

Final Amount = $130000.00 + $215741.64 = $345741.64

Deposits are added at month-start. Interest is calculated and compounded monthly.

How This Compound Interest Calculator Works

Enter an initial deposit, monthly contribution, annual rate before compounding, and a term in years and months. Each contribution is added at the beginning of the month. Changing the compounding frequency changes when interest compounds, not how often you contribute.

For example, start with $1,000, add $100 at the beginning of each month, and use a fixed annual rate of 12% compounded monthly. After one year, the projected balance is $2,407.76: $2,200 in deposits and $207.76 in interest. This rate is an example assumption, not a forecast.

The growth chart and table use the same monthly calculation. Total contributions include the initial deposit and all monthly additions; interest is the final balance minus those contributions. A term ending partway through a year includes a final partial-year row. At 0% interest, the balance is simply the sum of your deposits.

Daily compounding uses a fixed 365-day year and January–December month lengths without leap days. Quarterly, semi-annual, and annual modes accrue interest monthly and add it to the balance at the selected interval. Accrued interest remaining at the end is included in the final balance. For more examples, read Compound Interest Explained or Compound Interest in Real Life.

Results use a fixed rate and do not deduct taxes, fees, or inflation. Actual returns can vary. Use the CD calculator for certificate-of-deposit estimates or the investment calculator for broader investment planning.

Frequently Asked Questions

What is the difference between simple and compound interest?

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus all accumulated interest. Over time, compound interest grows exponentially while simple interest grows linearly.

Why might another calculator show a different result?

Check deposit timing, whether the quoted rate already includes compounding, and how interest accrues between compounding dates. This tool adds contributions at month-start; month-end contributions generally earn less at a positive rate. Daily calculations and partial periods can also differ between providers.

What is the Rule of 72?

The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by the annual interest rate. For example, at 8% return, your money doubles in approximately 72/8 = 9 years.