How to excess value in .Aspx page in ASP.Net

Question

I have code in .cs page

var startDate = new DateTime(now.Year, now.Month, 1);
ar endDate = startDate.AddMonths(1).AddDays(-1);

 How to excess these two values in .aspx page.As I am using

 

<%=startDate %>

 But it gives an error that name does not exist in the current context. What to do??