using System.Globalization;
public static void Main()
string s1 = "07-01-2021";
string s2 = "09-14-2021";
Console.WriteLine(Convert.ToDateTime(s1).ToString("ddMMMyyyy"));
Console.WriteLine(Convert.ToDateTime(s2).ToString("ddMMMyyyy"));
Console.WriteLine("week no "+(GetWeekNo(Convert.ToDateTime(s1),Convert.ToDateTime(s2))));
public static int GetWeekNo(DateTime d1, DateTime d2, DayOfWeek startOfWeek = DayOfWeek.Monday)
var diff = d2.Subtract(d1);
var weeks = (int)diff.Days / 7;
var remainingDays = diff.Days % 7;
var cal = CultureInfo.InvariantCulture.Calendar;
var d1WeekNo = cal.GetWeekOfYear(d1, CalendarWeekRule.FirstFullWeek, startOfWeek);
var d1PlusRemainingWeekNo = cal.GetWeekOfYear(d1.AddDays(remainingDays), CalendarWeekRule.FirstFullWeek, startOfWeek);
if (d1WeekNo != d1PlusRemainingWeekNo)