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Compound interest calculator

How a balance grows with monthly deposits and compounding.

Reviewed by Victor Yuki Matusita on . First published .

Your numbers stay on your device
$
$
%
years

Final balance

$171,714

You put in $82,000 and earn $89,714 of interest over 20 years at 6% compounded monthly.

  • Your deposits $82,000 · 48%
  • Interest $89,714 · 52%

Compounding and deposits

Deposits at the
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Growth by year

How to use the compound interest calculator

  1. Enter what you start with and what you add each month.
  2. Type a yearly rate and the number of years.
  3. Pick the compounding and whether you deposit at the start or the end of each month.
  4. Open the table by year, or save it as a PDF or a CSV.

How compound interest is worked out

The formula

The monthly rate is j = (1 + r ÷ n)^(n ÷ 12) − 1, where r is the yearly rate and n the times it compounds a year. Each month: balance = balance + balance × j + deposit, with the interest rounded to the cent.

Without deposits this is the familiar A = P × (1 + r ÷ n)^(n × t). The table adds up the deposits and the interest of each year.

Assumptions

  • The yearly rate is a nominal rate, compounded the number of times a year you choose.
  • Interest is added once a month at the monthly rate that compounding gives, (1 + rate ÷ n)^(n ÷ 12) − 1, rounded to the cent. With monthly compounding that is exactly the rate divided by 12.
  • Deposits are the same every month, at the start or at the end of the month.
  • No taxes, fees or withdrawals are included.

Worked example

This is the example the calculator opens with, worked out by the same engine you use above.

You enter
Starting amount$10,000.00
Monthly deposit$300.00
Yearly rate6%
Years20 years
Compoundingmonthly
Deposits at theEnd of the month
You get
Final balance$171,714.33
Your deposits$82,000.00
Interest$89,714.33

You put in $82,000 and earn $89,714 of interest over 20 years at 6% compounded monthly.

Sources

Educational tool

This calculator is an educational tool, not financial advice. Real returns change, and no rate here is a promise.

Questions about compound interest

What does compounding more often change?

Interest starts earning interest sooner. At the same yearly rate, daily compounding grows a little faster than yearly; the difference shows in the APY, the rate after compounding.

Should I deposit at the start or the end of the month?

A deposit at the start earns one more month of interest. Switch the choice to see how much that adds over the years.

Why does the calculator add interest monthly even with yearly compounding?

Deposits are monthly, so the balance is updated every month at the monthly rate that gives the same yearly result. It is a declared convention, so a bank statement can differ by a few cents.

Is the rate a return I can expect?

No. It is a number you choose to see what it would do. A savings account pays a stated rate; an investment can earn more, less or lose money.

Privacy

Your numbers stay on your device. The calculator runs in your browser, so nothing you type is sent anywhere, and the link you copy keeps the numbers after the #, a part of the address your browser never sends.