- Enter the opening balance and monthly deposit.
- Set the quoted annual rate and investment period.
- Choose how often interest compounds.
- Compare contributions with interest earned in the result details.
Compound Interest Calculator
Project the future value of a starting deposit plus regular monthly contributions. Compare the selected compounding schedule with the amount you contribute and see how much of the ending balance comes from accumulated interest.
Planning assumptions
$
$
%
years
Result
—
Projected future value
Total contributions—
Interest earned—
Effective annual yield—
Balance without interest—
FV principal = P(1 + r/n)nt
Monthly deposits are modeled at month-end using the equivalent monthly rate derived from the chosen compounding frequency.
What the result means
The headline combines the grown starting balance and all monthly deposits. Interest earned is the amount above total cash contributed.
The rate is assumed constant. Taxes, withdrawals, fees, and variable rates are not included.
$25,000 plus $500 at the end of each month for 20 years at 6% compounded monthly grows to about $313,776. Total contributed cash is $145,000, leaving about $168,776 of interest.
How are monthly contributions handled with annual compounding?
The selected compounding frequency is converted to an equivalent monthly rate, and deposits are added at the end of each month.
What happens when the interest rate is zero?
The future value equals the starting principal plus all monthly contributions, with no interest earned.
Does daily compounding make a large difference?
The difference is usually modest at ordinary rates, but it grows with the rate, balance, and investment period.
Are contributions assumed at the beginning or end of the month?
They are modeled at the end of each month, so a beginning-of-month deposit schedule would produce a slightly higher result.
Can this calculator model a negative rate?
Yes, within the allowed range, provided the equivalent periodic growth factor remains valid.