How can I calculate/find the week-number of a given date?

by 
var currentCulture = CultureInfo.CurrentCulture;
var weekNo = currentCulture.Calendar.GetWeekOfYear(
                new DateTime(2013, 12, 31),
                currentCulture.DateTimeFormat.CalendarWeekRule,
                currentCulture.DateTimeFormat.FirstDayOfWeek);

Be aware that this is not ISO 8601 compatible. In Sweden we use ISO 8601 week numbers but even though the culture is set to “sv-SE”, CalendarWeekRule is FirstFourDayWeek, and FirstDayOfWeek is Monday the weekNo variable will be set to 53 instead of the correct 1 in the above code.

I have only tried this with Swedish settings but I’m pretty sure that all countries (Austria, Germany, Switzerland and more) using ISO 8601 week numbers will be affected by this problem.

Peter van Ooijen and Shawn Steele has different solutions to this problem.

Here’s a compact solution

private static int WeekOfYearISO8601(DateTime date)
{
    var day = (int)CultureInfo.CurrentCulture.Calendar.GetDayOfWeek(date);
    return CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date.AddDays(4 - (day == 0 ? 7 : day)), CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

It’s been tested for the following dates

var datesAndISO8601Weeks = new Dictionary<DateTime, int>
                        {
                            {new DateTime(2000, 12, 31), 52},
                            {new DateTime(2001, 1, 1), 1},
                            {new DateTime(2005, 1, 1), 53},
                            {new DateTime(2007, 12, 31), 1},
                            {new DateTime(2008, 12, 29), 1},
                            {new DateTime(2010, 1, 3), 53},
                            {new DateTime(2011, 12, 31), 52},
                            {new DateTime(2012, 1, 1), 52},
                            {new DateTime(2013, 1, 2), 1},
                            {new DateTime(2013, 12, 31), 1},
                        };

foreach (var dateWeek in datesAndISO8601Weeks)
{
    Debug.Assert(WeekOfYearISO8601(dateWeek.Key) == dateWeek.Value, dateWeek.Key.ToShortDateString() + " should be week number " + dateWeek.Value + " but was " + WeekOfYearISO8601(dateWeek.Key));
}

More Related Contents:

  1. Days between two dates in asp.net
  2. Get the correct week number of a given date
  3. Specify Date format in MVC5 (dd/MM/yyyy)
  4. encrypt asp.net C# full config file [closed]
  5. How to make an algorithm to get all column names from across tables that relations with their primary key in SQL Server and C#?
  6. Loop through enum result property
  7. Parse JSON in C#
  8. Unable to cast object of type ‘System.DBNull’ to type ‘System.String`
  9. “The Controls collection cannot be modified because the control contains code blocks”
  10. Calling JavaScript Function From CodeBehind
  11. Datetime – Get next tuesday
  12. Catching “Maximum request length exceeded”
  13. Debug vs. release in .NET
  14. Asp.NET Identity 2 giving “Invalid Token” error
  15. What’s the difference between the WebConfigurationManager and the ConfigurationManager?
  16. Is it secure to store passwords in cookies?
  17. Read from word document line by line
  18. ASP.NET Web Application Message Box
  19. How can I use Dependency Injection in a .Net Core ActionFilterAttribute?
  20. Nested Repeaters in ASP.NET
  21. Getting a POST variable
  22. C#, FindControl [duplicate]
  23. Restrict route to controller namespace in ASP.NET Core
  24. Application_Error in global.asax not catching errors in WebAPI
  25. Validating file types by regular expression
  26. Unable to serialize the session state
  27. No IUserTokenProvider is registered
  28. How do static properties work in an asp.net environment?
  29. Performance cost of a try/catch block [duplicate]
  30. Convert string to datetime Using C#

Leave a Comment