=NPER(0,250/3,-5000)

where 0 is the interest rate for each period, 250/3 [=$83.33] the payment for each period and -5000 is the amount of the loan (shown as a negative number).

For this example you'll get an answer of 60. To convert that to an end date then, assuming start date in A1and that each period is a month

=DATE(YEAR(A1),MONTH(A1)+N

regards, barry