# How to derive date for Monday from the given week number?

Hi All,

There is a week number given and i need to find the starting date(i.e, Monday date) for that particular week. Can anyone help me with this.

Thanks,
Jeny Jasmine

Code in C#

`````` public static DateTime FirstDateOfWeekISO8601(int year, int weekOfYear)
{
DateTime jan1 = new DateTime(year, 1, 1);
int daysOffset = DayOfWeek.Thursday - jan1.DayOfWeek;

// Use first Thursday in January to get first week of the year as
// it will never be in Week 52/53
DateTime firstThursday = jan1.AddDays(daysOffset);
var cal = CultureInfo.CurrentCulture.Calendar;
int firstWeek = cal.GetWeekOfYear(firstThursday, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);

var weekNum = weekOfYear;
// As we're adding days to a date in Week 1,
// we need to subtract 1 in order to get the right date for week #1
if (firstWeek == 1)
{
weekNum -= 1;
}

// Using the first Thursday as starting week ensures that we are starting in the right year
// then we add number of weeks multiplied with days
var result = firstThursday.AddDays(weekNum * 7);

// Subtract 3 days from Thursday to get Monday, which is the first weekday in ISO8601
}
``````
1 Like

Hey @jeny

You can refer to an old existing Thread for your reference: - Date of Monday in the current week

Note:- Search forum before posting your queries, In most of the cases you will find an existing solution thread on the forum

Regardsâ€¦!!
Aksh

1 Like

Thanks Akshay and Karthikâ€¦will try the above solutionsâ€¦!!