Calculate the start-date and name of a quarter from a given date

Question

How can I find the start-date and name (1, 2, 3, etc.) of a quarter from a given date?

Answer 1

Something like (untested):

DateTime date;
int quarterNumber = (date.Month-1)/3+1;
DateTime firstDayOfQuarter = new DateTime(date.Year, (quarterNumber-1)*3+1,1);
DateTime lastDayOfQuarter = firstDayOfQuarter.AddMonths(3).AddDays(-1);

Answer 2

A simpler two liner with live demo here + press F8 to run .

var date = DateTime.Now; //Give you own DateTime
int offset = 2, monthsInQtr = 3;

var quarter = (date.Month + offset) / monthsInQtr; //To find which quarter 
var totalMonths = quarter * monthsInQtr;

var startDateInQtr = new DateTime(date.Year, totalMonths - offset, 1); //start date in quarter 

If you are looking at last day of the quarter use DateTime.DaysInMonth

var endDateInQtr = new DateTime(date.Year, totalMonths, DateTime.DaysInMonth(date.Year, totalMonths));