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copied!<p>You can use following two methods to calculate the week-number and the start-date of a given weeknumber according to a given year:</p> <pre><code>// this method is borrowed from http://stackoverflow.com/a/11155102/284240 public static int GetIso8601WeekOfYear(DateTime time) { DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time); if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday) { time = time.AddDays(3); } return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday); } public static DateTime FirstDateOfWeek(int year, int weekOfYear, System.Globalization.CultureInfo ci) { DateTime jan1 = new DateTime(year, 1, 1); int daysOffset = (int)ci.DateTimeFormat.FirstDayOfWeek - (int)jan1.DayOfWeek; DateTime firstWeekDay = jan1.AddDays(daysOffset); int firstWeek = ci.Calendar.GetWeekOfYear(jan1, ci.DateTimeFormat.CalendarWeekRule, ci.DateTimeFormat.FirstDayOfWeek); if ((firstWeek <= 1 || firstWeek >= 52) && daysOffset >= -3) { weekOfYear -= 1; } return firstWeekDay.AddDays(weekOfYear * 7); } </code></pre> <p>Then you can get both dates in the following way:</p> <pre><code>// 46 int thisWeekNumber = GetIso8601WeekOfYear(DateTime.Today); // 11/11/2013 DateTime firstDayOfWeek= FirstDateOfWeek(2013, thisWeekNumber, CultureInfo.CurrentCulture); // 11/12/2012 DateTime firstDayOfLastYearWeek = FirstDateOfWeek(2012, thisWeekNumber, CultureInfo.CurrentCulture); </code></pre> <p>Add 6 days to get the end of the week.</p>

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