Week numbers in C#

Support for ISO week numbers was added in .NET 5.0.

How to get the week number from a date

To get the ISO week number (1-53) from a System.DateTime instance, use System.Globalization.ISOWeek.GetWeekOfYear(date).

To get the corresponding four-digit year (e.g. 2022), use System.Globalization.ISOWeek.GetYear(date).

Read more about ISOWeek.GetWeekOfYear() and ISOWeek.GetYear() in the .NET API documentation.

How to get the date from a week number

To get the start time of a week (Monday at midnight), use System.Globalization.ISOWeek.ToDateTime(year, week, DayOfWeek.Monday)).

year is a 4-digit year (e.g. 2022), and week is an ISO week number (1-53).

Read more about ISOWeek.ToDateTime() in the .NET API documentation.

How to get the number of weeks in a year

To get the number of ISO weeks in a year (i.e. the number of the last week), use System.Globalization.ISOWeek.GetWeeksInYear(year).

Read more about ISOWeek.GetWeeksInYear() in the .NET API documentation.