Return the date of the first Monday of any year with this UDF ISO Year function in Excel. This is a really simple and easy to use UDF (user defined function) in Excel. You just input the desired year, in 4 digit format (1996, 2001, etc.) and the function will return the date of the first Monday in that year.
Make sure the cell where the function is located is formatted as a date because the result of the function is a date serial number.
Function ISOYEARSTART(Year As Integer) As Date
Dim WeekDay As Integer
Dim NewYear As Date
NewYear = DateSerial(Year, 1, 1)
WeekDay = (NewYear - 2) Mod 7
If WeekDay < 4 Then
ISOYEARSTART = NewYear - WeekDay
Else
ISOYEARSTART = NewYear - WeekDay + 7
End If
End Function