VB6Parse / Library / Datetime / weekday

VB6 Weekday Function The Weekday function returns a Variant (Integer) specifying a whole number representing the day of the week.

Syntax

Weekday(date[, firstdayofweek])

Parameters

• date: Required. Variant, numeric expression, string expression, or any combination that can represent a date. If date contains Null, Null is returned.
• firstdayofweek: Optional. A constant that specifies the first day of the week. If not specified, vbSunday is assumed.

FirstDayOfWeek Constants

• vbUseSystem (0): Use the system setting
• vbSunday (1): Sunday (default)
• vbMonday (2): Monday
• vbTuesday (3): Tuesday
• vbWednesday (4): Wednesday
• vbThursday (5): Thursday
• vbFriday (6): Friday
• vbSaturday (7): Saturday

Returns

Returns a Variant (Integer) from 1 to 7 representing the day of the week: - When firstdayofweek is vbSunday (default): 1=Sunday, 2=Monday, 3=Tuesday, 4=Wednesday, 5=Thursday, 6=Friday, 7=Saturday - When firstdayofweek is vbMonday: 1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday - The numbering adjusts based on which day is specified as the first day of the week

Remarks

The Weekday function determines which day of the week a date falls on: - Return value range: Always 1-7, where 1 represents the first day of the week - Default first day: Sunday (vbSunday = 1) if not specified - Null handling: Returns Null if date contains Null - Date parsing: Accepts various date formats (strings, numbers, Date types) - Zero-based alternative: Use (Weekday(date) - 1) for 0-6 range if needed - System setting: vbUseSystem (0) uses Windows regional settings - International support: firstdayofweek allows cultural calendar preferences - Combine with DateSerial: Calculate specific weekdays

Understanding Return Values

The return value changes based on firstdayofweek: - With vbSunday (default): Sunday=1, Monday=2, ..., Saturday=7 - With vbMonday: Monday=1, Tuesday=2, ..., Sunday=7 - With vbTuesday: Tuesday=1, Wednesday=2, ..., Monday=7 - And so on for other starting days

Common Usage Patterns

• Weekend detection: Weekday(date) = vbSaturday Or Weekday(date) = vbSunday
• Weekday detection: Weekday(date) >= vbMonday And Weekday(date) <= vbFriday
• Specific day check: Weekday(date) = vbMonday
• ISO week (Monday start): Use Weekday(date, vbMonday)

Typical Uses

1. Weekend Detection: Determine if a date is Saturday or Sunday
2. Business Day Calculation: Check if date is a weekday
3. Schedule Planning: Plan events for specific days of the week
4. Report Grouping: Group data by day of week
5. Calendar Display: Format calendars with proper day alignment
6. Work Week Calculations: Calculate working days
7. Day Name Display: Get day name with WeekdayName function
8. Date Validation: Ensure dates fall on specific days

Basic Examples

Example 1: Check if Date is Weekend

Function IsWeekend(checkDate As Date) As Boolean
    Dim dayNum As Integer
    dayNum = Weekday(checkDate)
    IsWeekend = (dayNum = vbSaturday Or dayNum = vbSunday)
End Function
' Usage:
If IsWeekend(Date) Then
    MsgBox "It's the weekend!"
End If

Example 2: Get Day Name

Function GetDayName(checkDate As Date) As String
    Select Case Weekday(checkDate)
        Case vbSunday
            GetDayName = "Sunday"
        Case vbMonday
            GetDayName = "Monday"
        Case vbTuesday
            GetDayName = "Tuesday"
        Case vbWednesday
            GetDayName = "Wednesday"
        Case vbThursday
            GetDayName = "Thursday"
        Case vbFriday
            GetDayName = "Friday"
        Case vbSaturday
            GetDayName = "Saturday"
    End Select
End Function

Example 3: Find Next Monday

Function GetNextMonday(fromDate As Date) As Date
    Dim daysToAdd As Integer
    Dim currentDay As Integer
    currentDay = Weekday(fromDate)
    If currentDay = vbMonday Then
        daysToAdd = 7 ' Next Monday is 7 days away
    ElseIf currentDay < vbMonday Then
        daysToAdd = vbMonday - currentDay
    Else
        daysToAdd = 7 - (currentDay - vbMonday)
    End If
    GetNextMonday = fromDate + daysToAdd
End Function

Example 4: Count Weekdays in Month

Function CountWeekdaysInMonth(year As Integer, month As Integer) As Integer
    Dim currentDate As Date
    Dim lastDay As Integer
    Dim day As Integer
    Dim count As Integer
    lastDay = Day(DateSerial(year, month + 1, 0))
    count = 0
    For day = 1 To lastDay
        currentDate = DateSerial(year, month, day)
        If Weekday(currentDate) >= vbMonday And Weekday(currentDate) <= vbFriday Then
            count = count + 1
        End If
    Next day
    CountWeekdaysInMonth = count
End Function

Common Patterns

Pattern 1: Is Business Day

Function IsBusinessDay(checkDate As Date) As Boolean
    Dim dayNum As Integer
    dayNum = Weekday(checkDate)
    IsBusinessDay = (dayNum >= vbMonday And dayNum <= vbFriday)
End Function

Pattern 2: Get Week Start (Monday)

Function GetWeekStart(anyDate As Date) As Date
    Dim dayNum As Integer
    dayNum = Weekday(anyDate, vbMonday)
    GetWeekStart = anyDate - (dayNum - 1)
End Function

Pattern 3: Get Week End (Sunday)

Function GetWeekEnd(anyDate As Date) As Date
    Dim dayNum As Integer
    dayNum = Weekday(anyDate, vbMonday)
    GetWeekEnd = anyDate + (7 - dayNum)
End Function

Pattern 4: Days Until Specific Weekday

Function DaysUntilWeekday(fromDate As Date, targetDay As Integer) As Integer
    Dim currentDay As Integer
    currentDay = Weekday(fromDate)
    If targetDay >= currentDay Then
        DaysUntilWeekday = targetDay - currentDay
    Else
        DaysUntilWeekday = 7 - (currentDay - targetDay)
    End If
End Function

Pattern 5: Is Specific Day

Function IsMonday(checkDate As Date) As Boolean
    IsMonday = (Weekday(checkDate) = vbMonday)
End Function
Function IsFriday(checkDate As Date) As Boolean
    IsFriday = (Weekday(checkDate) = vbFriday)
End Function

Pattern 6: Add Business Days

Function AddBusinessDays(startDate As Date, daysToAdd As Integer) As Date
    Dim currentDate As Date
    Dim daysAdded As Integer
    currentDate = startDate
    daysAdded = 0
    Do While daysAdded < daysToAdd
        currentDate = currentDate + 1
        If Weekday(currentDate) >= vbMonday And Weekday(currentDate) <= vbFriday Then
            daysAdded = daysAdded + 1
        End If
    Loop
    AddBusinessDays = currentDate
End Function

Pattern 7: Group by Day of Week

Function GetDayOfWeekGroup(checkDate As Date) As String
    Select Case Weekday(checkDate)
        Case vbMonday, vbWednesday, vbFriday
            GetDayOfWeekGroup = "MWF"
        Case vbTuesday, vbThursday
            GetDayOfWeekGroup = "TTh"
        Case vbSaturday, vbSunday
            GetDayOfWeekGroup = "Weekend"
    End Select
End Function

Pattern 8: Calculate Days in Same Week

Function AreSameWeek(date1 As Date, date2 As Date) As Boolean
    Dim week1Start As Date
    Dim week2Start As Date
    week1Start = date1 - (Weekday(date1, vbMonday) - 1)
    week2Start = date2 - (Weekday(date2, vbMonday) - 1)
    AreSameWeek = (week1Start = week2Start)
End Function

Pattern 9: Next Occurrence of Weekday

Function NextOccurrenceOf(targetDay As Integer, Optional fromDate As Date) As Date
    Dim startDate As Date
    Dim daysToAdd As Integer
    If fromDate = 0 Then startDate = Date Else startDate = fromDate
    daysToAdd = DaysUntilWeekday(startDate, targetDay)
    If daysToAdd = 0 Then daysToAdd = 7 ' Next occurrence
    NextOccurrenceOf = startDate + daysToAdd
End Function

Pattern 10: Weekend Days in Range

Function CountWeekendDays(startDate As Date, endDate As Date) As Integer
    Dim currentDate As Date
    Dim count As Integer
    count = 0
    currentDate = startDate
    Do While currentDate <= endDate
        If Weekday(currentDate) = vbSaturday Or Weekday(currentDate) = vbSunday Then
            count = count + 1
        End If
        currentDate = currentDate + 1
    Loop
    CountWeekendDays = count
End Function

Advanced Usage

Example 1: Business Day Calculator Class

' Class: BusinessDayCalculator
' Calculates business days excluding weekends and holidays
Option Explicit
Private m_Holidays() As Date
Private m_HolidayCount As Integer
Public Sub Initialize()
    m_HolidayCount = 0
    ReDim m_Holidays(0 To 9)
End Sub
Public Sub AddHoliday(holidayDate As Date)
    If m_HolidayCount > UBound(m_Holidays) Then
        ReDim Preserve m_Holidays(0 To UBound(m_Holidays) * 2)
    End If
    m_Holidays(m_HolidayCount) = holidayDate
    m_HolidayCount = m_HolidayCount + 1
End Sub
Public Function IsBusinessDay(checkDate As Date) As Boolean
    Dim i As Integer
    ' Check if weekend
    If Weekday(checkDate) = vbSaturday Or Weekday(checkDate) = vbSunday Then
        IsBusinessDay = False
        Exit Function
    End If
    ' Check if holiday
    For i = 0 To m_HolidayCount - 1
        If Int(m_Holidays(i)) = Int(checkDate) Then
            IsBusinessDay = False
            Exit Function
        End If
    Next i
    IsBusinessDay = True
End Function
Public Function CountBusinessDays(startDate As Date, endDate As Date) As Integer
    Dim currentDate As Date
    Dim count As Integer
    count = 0
    currentDate = startDate
    Do While currentDate <= endDate
        If IsBusinessDay(currentDate) Then
            count = count + 1
        End If
        currentDate = currentDate + 1
    Loop
    CountBusinessDays = count
End Function
Public Function AddBusinessDays(startDate As Date, daysToAdd As Integer) As Date
    Dim currentDate As Date
    Dim daysAdded As Integer
    currentDate = startDate
    daysAdded = 0
    Do While daysAdded < daysToAdd
        currentDate = currentDate + 1
        If IsBusinessDay(currentDate) Then
            daysAdded = daysAdded + 1
        End If
    Loop
    AddBusinessDays = currentDate
End Function

Example 2: Week Navigator Module

' Module: WeekNavigator
' Navigate by weeks with different starting days
Option Explicit
Public Function GetWeekStart(anyDate As Date, _
                            Optional firstDayOfWeek As VbDayOfWeek = vbMonday) As Date
    Dim dayNum As Integer
    dayNum = Weekday(anyDate, firstDayOfWeek)
    GetWeekStart = anyDate - (dayNum - 1)
End Function
Public Function GetWeekEnd(anyDate As Date, _
                          Optional firstDayOfWeek As VbDayOfWeek = vbMonday) As Date
    Dim dayNum As Integer
    dayNum = Weekday(anyDate, firstDayOfWeek)
    GetWeekEnd = anyDate + (7 - dayNum)
End Function
Public Function GetPreviousWeekStart(anyDate As Date, _
                                    Optional firstDayOfWeek As VbDayOfWeek = vbMonday) As Date
    GetPreviousWeekStart = GetWeekStart(anyDate - 7, firstDayOfWeek)
End Function
Public Function GetNextWeekStart(anyDate As Date, _
                                Optional firstDayOfWeek As VbDayOfWeek = vbMonday) As Date
    GetNextWeekStart = GetWeekStart(anyDate + 7, firstDayOfWeek)
End Function
Public Function GetDaysInWeek(weekStartDate As Date, _
                             Optional firstDayOfWeek As VbDayOfWeek = vbMonday) As Date()
    Dim days(0 To 6) As Date
    Dim i As Integer
    Dim startDate As Date
    startDate = GetWeekStart(weekStartDate, firstDayOfWeek)
    For i = 0 To 6
        days(i) = startDate + i
    Next i
    GetDaysInWeek = days
End Function

Example 3: Schedule Analyzer Class

' Class: ScheduleAnalyzer
' Analyzes date schedules and patterns
Option Explicit
Public Function GetDayDistribution(dates() As Date) As Variant
    Dim distribution(1 To 7) As Integer
    Dim i As Long
    Dim dayNum As Integer
    For i = LBound(dates) To UBound(dates)
        dayNum = Weekday(dates(i))
        distribution(dayNum) = distribution(dayNum) + 1
    Next i
    GetDayDistribution = distribution
End Function
Public Function GetMostCommonDay(dates() As Date) As Integer
    Dim distribution As Variant
    Dim maxCount As Integer
    Dim mostCommonDay As Integer
    Dim i As Integer
    distribution = GetDayDistribution(dates)
    maxCount = 0
    mostCommonDay = vbSunday
    For i = 1 To 7
        If distribution(i) > maxCount Then
            maxCount = distribution(i)
            mostCommonDay = i
        End If
    Next i
    GetMostCommonDay = mostCommonDay
End Function
Public Function FilterByWeekday(dates() As Date, targetDay As Integer) As Date()
    Dim result() As Date
    Dim count As Long
    Dim i As Long
    count = 0
    For i = LBound(dates) To UBound(dates)
        If Weekday(dates(i)) = targetDay Then
            ReDim Preserve result(0 To count)
            result(count) = dates(i)
            count = count + 1
        End If
    Next i
    FilterByWeekday = result
End Function
Public Function IsRecurringPattern(dates() As Date, dayOfWeek As Integer) As Boolean
    Dim i As Long
    IsRecurringPattern = True
    For i = LBound(dates) To UBound(dates)
        If Weekday(dates(i)) <> dayOfWeek Then
            IsRecurringPattern = False
            Exit Function
        End If
    Next i
End Function

Example 4: Calendar Generator Module

' Module: CalendarGenerator
' Generates calendar grids and displays
Option Explicit
Public Function GenerateMonthCalendar(year As Integer, month As Integer, _
                                     Optional firstDayOfWeek As VbDayOfWeek = vbSunday) As Variant
    Dim calendar(0 To 5, 0 To 6) As Variant
    Dim firstDay As Date
    Dim lastDay As Date
    Dim currentDate As Date
    Dim row As Integer
    Dim col As Integer
    Dim dayNum As Integer
    firstDay = DateSerial(year, month, 1)
    lastDay = DateSerial(year, month + 1, 0)
    ' Initialize calendar with empty values
    For row = 0 To 5
        For col = 0 To 6
            calendar(row, col) = ""
        Next col
    Next row
    ' Fill in the days
    currentDate = firstDay
    Do While currentDate <= lastDay
        dayNum = Weekday(currentDate, firstDayOfWeek) - 1
        row = (Day(currentDate) + Weekday(firstDay, firstDayOfWeek) - 2) \ 7
        col = dayNum
        calendar(row, col) = Day(currentDate)
        currentDate = currentDate + 1
    Loop
    GenerateMonthCalendar = calendar
End Function
Public Function GetWeekNumbers(year As Integer, month As Integer) As Integer()
    Dim firstDay As Date
    Dim lastDay As Date
    Dim currentDate As Date
    Dim weekNums() As Integer
    Dim count As Integer
    firstDay = DateSerial(year, month, 1)
    lastDay = DateSerial(year, month + 1, 0)
    count = 0
    currentDate = firstDay
    Do While currentDate <= lastDay
        If Weekday(currentDate, vbMonday) = 1 Then
            ReDim Preserve weekNums(0 To count)
            weekNums(count) = DatePart("ww", currentDate, vbMonday, vbFirstFourDays)
            count = count + 1
        End If
        currentDate = currentDate + 1
    Loop
    GetWeekNumbers = weekNums
End Function

Error Handling

The Weekday function can raise the following errors: - Error 13 (Type mismatch): If date argument cannot be interpreted as a date - Error 5 (Invalid procedure call or argument): If firstdayofweek is not between 0 and 7 - Error 6 (Overflow): If date value is too large or too small

Performance Notes

• Very fast operation - direct calculation from date value
• No performance difference between firstdayofweek values
• Constant time O(1) operation
• Can be called repeatedly without performance concerns
• Consider caching result if used multiple times with same date

Best Practices

1. Use named constants (vbMonday, vbSunday, etc.) instead of numeric values for clarity
2. Specify firstdayofweek explicitly when week start matters (especially for ISO weeks)
3. Cache results when calling repeatedly with same date
4. Validate date input before calling Weekday to avoid errors
5. Use WeekdayName function to get localized day names
6. Document assumptions about which day starts the week in your code
7. Consider time zones when working with date/time values
8. Test boundary cases (month/year boundaries, leap years)
9. Use with DateAdd for complex date arithmetic
10. Handle Null values explicitly when working with Variant dates

Comparison Table

Platform Notes

• Available in VB6, VBA, and VBScript
• Behavior consistent across platforms
• Returns Integer (can be stored in Integer or Long)
• System locale affects vbUseSystem behavior
• Date range: January 1, 100 to December 31, 9999

Limitations

• Cannot directly return day name (use WeekdayName for that)
• Return value always 1-7 (no zero-based option)
• Cannot specify custom week numbering systems
• Does not account for holidays or business days
• No built-in ISO 8601 week numbering (use DatePart("ww", ...) for that)
• Cannot calculate week of year (use DatePart for that)