The formula for the future value of an investment with regular contributions is
FV = M((1+r/n)^(nt)-1)(n/r)
where
FV = Future value
M = Deposit per period
r = Interest rate
n = number of periods per year
t = number of years
So let's solve for M, then substitute the known values and calculate:
FV = M((1+r/n)^(nt)-1)(n/r)
FV/(((1+r/n)^(nt)-1)(n/r)) = M
250000/(((1+0.037/12)^(12 * 15)-1)(12/0.036)) = M
250000/(((1+0.003083333)^(180)-1)(324.3243243)) = M
250000/(((1.003083333)^(180)-1)(324.3243243)) = M
250000/((1.740454228-1)(324.3243243)) = M
250000/240.1473172 = M
1041.027661 = M
So the monthly deposit should be 1041.03 every month.
Note: This calculation assumes that the 1st deposit will happen AFTER the 1st month.
