Date Calculation:

Dim age_to_date As DateTime = DateTime.Parse(age_to.Text)
Dim age_from_date As DateTime = DateTime.Parse(age_from.Text)

Dim age_to_ As DateTime = Convert.ToDateTime(age_to_date)
Dim year_to As String = age_to_.Year.ToString()
Dim month_to As String = age_to_.Month()
Dim day_to As String = age_to_.Day()

Dim age_from_ As DateTime = Convert.ToDateTime(age_from_date)
Dim year_from As String = age_from_.Year.ToString()
Dim month_from As String = age_from_.Month()
Dim day_from As String = age_from_.Day()

Dim age_years As Integer = Math.Abs(Convert.ToInt16(year_to) - Convert.ToInt16(year_from))
Dim age_months As Integer = Math.Abs(Convert.ToInt16(month_to) - Convert.ToInt16(month_from))
Dim age_days As Integer = Math.Abs(Convert.ToInt16(day_to) - Convert.ToInt16(day_from))

display_age.Text = age_years.ToString() & " years " & age_months.ToString() & " months " & age_days.ToString() & " days"



Date Calculation:
Dim age_to_date As DateTime = DateTime.Parse(age_to.Text)
Dim age_from_date As DateTime = DateTime.Parse(age_from.Text)
Dim age_to_ As DateTime = Convert.ToDateTime(age_to_date)
Dim year_to As String = age_to_.Year.ToString()
Dim month_to As String = age_to_.Month()
Dim day_to As String = age_to_.Day()
Dim age_from_ As DateTime = Convert.ToDateTime(age_from_date)
Dim year_from As String = age_from_.Year.ToString()
Dim month_from As String = age_from_.Month()
Dim day_from As String = age_from_.Day()
Dim age_years As Integer = Math.Abs(Convert.ToInt16(year_to) - Convert.ToInt16(year_from))
Dim age_months As Integer = Math.Abs(Convert.ToInt16(month_to) - Convert.ToInt16(month_from))
Dim age_days As Integer = Math.Abs(Convert.ToInt16(day_to) - Convert.ToInt16(day_from))
display_age.Text = age_years.ToString() & " years " & age_months.ToString() & " months " & age_days.ToString() & " days"

Date time and week number of the year:
It gets the firstdate and lastdate on the asp.net calendar control Maybe that will help.

Dim firstDOW As DayOfWeek
If (Calendar1.FirstDayOfWeek = System.Web.UI.WebControls.FirstDayOfWeek.Default) Then
firstDOW = System.Globalization.DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek
Else
firstDOW = Calendar1.FirstDayOfWeek
End If
If (firstDOW = Calendar1.VisibleDate.DayOfWeek) Then
firstdate = firstdate.AddDays(-7)
Else
While (firstdate.DayOfWeek <> firstDOW)
firstdate = firstdate.AddDays(-1)
End While
End If

Dim lastdate As DateTime = firstdate.AddDays(41)

Date Time:
http://dotnetguts.blogspot.com/search/label/SQL