DateTime date = DateTime.Now;

//季起始结束日期

string starttime = date.AddMonths(-3 - ((date.Month - 1) % 3)).AddMonths(-15).ToString("yyyy-MM-01");

string endtime = date.AddMonths(0 - ((date.Month - 1) % 3)).AddDays(1 - date.Day).AddDays(-1).ToString("yyyy-MM-dd");

 

//或

DateTime dt= DateTime.Now;

DateTime starttime = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day); //本季度初

DateTime endtime = starttime.AddMonths(3).AddDays(-1);