NPER(rate,pmt,pv[,fv,type])
NPER calculates number of periods of an investment based on periodic constant payments and a constant interest rate.
The interest rate per period is rate, pmt is the payment made each period, pv is the present value, fv is the future value and type is when the payments are due. If type = 1, payments are due at the beginning of the period, if type = 0, payments are due at the end of the period.
For example, if you deposit $10,000 in a savings account that earns an interest rate of 6%. To calculate how many years it will take to double your investment use NPER as follows:
=NPER(0.06, 0, -10000, 20000,0)returns 11.895661046 which indicates that you can double your money just before the end of the 12th year.