What have you tried so far?
And anyways, it has nothing to do with C#/ASP.Net.
If you want, here is the formula to calculate EMI:
E = P * r * (1 + r)n / ((1 + r)n -1)
Here p = principal amount
r = interesr rate per month(ex: if interest rate per annum is 10% then 10/(12*100))
n = tenure in months
And
Google [
^]is anyways your friend.