"First, the variables:
FV = future value
A = one-time investment (not for annuities)
p = investment per compound period
i = interest rate
c = number of compound periods per year
n = number of compound periods
To get p, take the target amount to invest each month, multiply it by 12 to get a yearly investment amount, then divide by c to get the investment per compound period. To get n, take the number of years to invest and multiply it by c to get the number of compound periods.
Simple compound interest with one-time investments... This is the formula that will present the future value (FV) of an investment after n years if we invest A at i interest compounded c times per year:
FV = A (1 + i/c)(n)
Required current investment (A) to have FV in the future if the i interest is compounded c times per year for n years:
FV
A = -----------
(1 + i/c)n
The time period (n) to have FV in the future if the initial investment A at i interest compounded c times per year:
ln(FV) - ln(A)
n = ------------------
ln(c + i) - ln(c)
NOTE: ln is the natural logarithm function.
Enter your own amounts:"
See exactly how to calculate compound interest