How to do calculations in grid view based on date

Question

how to do emi calculation



for ex i have taken loan 50000

for 50000 i have to pay emi monthly 5000 for 10 months

start date is 1st Mar 2015
end date is 1st Dec 2015.

and i have inserted all these values in database those are
Name
TotalAmount
StartDate
EndDate
MonthlyPay

and i have binded these values to grid view also

my problem is , i want to show extra column in grid that is due amount ,when start date is crossed 1 month,show due amount is 5000 , and it crossed
2 months show 10000 and this so on for 10 months and then stop.


can you please suggest me how to do this, or give me any example for emi payment page,
if you want code i will attach