I stumbled across this the other day and I thought it was so slick I would share.
This example computes the DateTime for both the first and last day of the current month.
var monthStartDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1);
var monthEndDate = start.AddMonths(1).AddDays(-1);
You can take the range even further by changing the “AddMonths” number.
Pretty slick.