VBA supports 2 calendars : Gregorian and Hijri

The Calendar property is used to modify or display the current calendar.

The 2 values for the Calendar are:

Value	Constant	Description
0	vbCalGreg	Gregorian calendar (default)
1	vbCalHijri	Hijri calendar

Example

Sub CalendarExample()
    'Cache the current setting.
    Dim Cached As Integer
    Cached = Calendar

    ' Dates in Gregorian Calendar
    Calendar = vbCalGreg
    Dim Sample As Date
    'Create sample date of 2016-07-28
    Sample = DateSerial(2016, 7, 28)

    Debug.Print "Current Calendar : " & Calendar
    Debug.Print "SampleDate = " & Format$(Sample, "yyyy-mm-dd")
    
    ' Date in Hijri Calendar
    Calendar = vbCalHijri
    Debug.Print "Current Calendar : " & Calendar
    Debug.Print "SampleDate = " & Format$(Sample, "yyyy-mm-dd")
    
    'Reset VBA to cached value.
    Cached = Calendar
End Sub

This Sub prints the following ;

Current Calendar : 0
SampleDate = 2016-07-28
Current Calendar : 1
SampleDate = 1437-10-23

Retrieve System DateTime

VBA supports 3 built-in functions to retrieve the date and/or time from the system's clock.

Function	Return Type	Return Value
Now	Date	Returns the current date and time
Date	Date	Returns the date portion of the current date and time
Time	Date	Returns the time portion of the current date and time

Sub DateTimeExample()

    ' -----------------------------------------------------
    ' Note : EU system with default date format DD/MM/YYYY
    ' -----------------------------------------------------
    
    Debug.Print Now   ' prints 28/07/2016 10:16:01 (output below assumes this date and time)
    Debug.Print Date  ' prints 28/07/2016
    Debug.Print Time  ' prints 10:16:01
    
    ' Apply a custom format to the current date or time
    Debug.Print Format$(Now, "dd mmmm yyyy hh:nn")  ' prints 28 July 2016 10:16
    Debug.Print Format$(Date, "yyyy-mm-dd")         ' prints 2016-07-28
    Debug.Print Format$(Time, "hh") & " hour " & _
                Format$(Time, "nn") & " min " & _
                Format$(Time, "ss") & " sec "       ' prints 10 hour 16 min 01 sec
    
End Sub

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Timer Function

The Timer function returns a Single representing the number of seconds elapsed since midnight. The precision is one hundredth of a second.

Sub TimerExample()

    Debug.Print Time    ' prints 10:36:31  (time at execution)
    Debug.Print Timer   ' prints 38191,13  (seconds since midnight)

End Sub

Because Now and Time functions are only precise to seconds, Timer offers a convenient way to increase accuracy of time measurement:

Sub GetBenchmark()
       
    Dim StartTime  As Single
    StartTime = Timer       'Store the current Time
    
    Dim i As Long
    Dim temp As String
    For i = 1 To 1000000    'See how long it takes Left$ to execute 1,000,000 times
        temp = Left$("Text", 2)
    Next i
    
    Dim Elapsed As Single
    Elapsed = Timer - StartTime
    Debug.Print "Code completed in " & CInt(Elapsed * 1000) & " ms"

End Sub

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IsDate()

IsDate() tests whether an expression is a valid date or not. Returns a Boolean.

Sub IsDateExamples()

    Dim anything As Variant
       
    anything = "September 11, 2001"

    Debug.Print IsDate(anything)    'Prints True
            
    anything = #9/11/2001#

    Debug.Print IsDate(anything)    'Prints True
   
    anything = "just a string"

    Debug.Print IsDate(anything)    'Prints False

    anything = vbNull
    
    Debug.Print IsDate(anything)    'Prints False
    
End Sub

These functions take a Variant that can be cast to a Date as a parameter and return an Integer representing a portion of a date or time. If the parameter can not be cast to a Date, it will result in a run-time error 13: Type mismatch.

Function	Description	Returned value
Year()	Returns the year portion of the date argument.	Integer (100 to 9999)
Month()	Returns the month portion of the date argument.	Integer (1 to 12)
Day()	Returns the day portion of the date argument.	Integer (1 to 31)
WeekDay()	Returns the day of the week of the date argument. Accepts an optional second argument definining the first day of the week	Integer (1 to 7)
Hour()	Returns the hour portion of the date argument.	Integer (0 to 23)
Minute()	Returns the minute portion of the date argument.	Integer (0 to 59)
Second()	Returns the second portion of the date argument.	Integer (0 to 59)

Examples:

Sub ExtractionExamples()

    Dim MyDate As Date
    
    MyDate = DateSerial(2016, 7, 28) + TimeSerial(12, 34, 56)

    Debug.Print Format$(MyDate, "yyyy-mm-dd hh:nn:ss") ' prints 2016-07-28 12:34:56

    Debug.Print Year(MyDate)                           ' prints 2016
    Debug.Print Month(MyDate)                          ' prints 7
    Debug.Print Day(MyDate)                            ' prints 28
    Debug.Print Hour(MyDate)                           ' prints 12
    Debug.Print Minute(MyDate)                         ' prints 34
    Debug.Print Second(MyDate)                         ' prints 56
    
    Debug.Print Weekday(MyDate)                        ' prints 5
    'Varies by locale - i.e. will print 4 in the EU and 5 in the US
    Debug.Print Weekday(MyDate, vbUseSystemDayOfWeek)
    Debug.Print Weekday(MyDate, vbMonday)              ' prints 4
    Debug.Print Weekday(MyDate, vbSunday)              ' prints 5
    
End Sub

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DatePart() Function

DatePart() is also a function returning a portion of a date, but works differently and allow more possibilities than the functions above. It can for instance return the Quarter of the year or the Week of the year.

Syntax:

DatePart ( interval, date  [, firstdayofweek] [, firstweekofyear] )

interval argument can be :

Interval	Description
"yyyy"	Year (100 to 9999)
"y"	Day of the year (1 to 366)
"m"	Month (1 to 12)
"q"	Quarter (1 to 4)
"ww"	Week (1 to 53)
"w"	Day of the week (1 to 7)
"d"	Day of the month (1 to 31)
"h"	Hour (0 to 23)
"n"	Minute (0 to 59)
"s"	Second (0 to 59)

firstdayofweek is optional. it is a constant that specifies the first day of the week. If not specified, vbSunday is assumed.

firstweekofyear is optional. it is a constant that specifies the first week of the year. If not specified, the first week is assumed to be the week in which January 1 occurs.

Examples:

Sub DatePartExample()

    Dim MyDate As Date
    
    MyDate = DateSerial(2016, 7, 28) + TimeSerial(12, 34, 56)

    Debug.Print Format$(MyDate, "yyyy-mm-dd hh:nn:ss") ' prints 2016-07-28 12:34:56
    
    Debug.Print DatePart("yyyy", MyDate)              ' prints 2016
    Debug.Print DatePart("y", MyDate)                 ' prints 210
    Debug.Print DatePart("h", MyDate)                 ' prints 12
    Debug.Print DatePart("Q", MyDate)                 ' prints 3
    Debug.Print DatePart("w", MyDate)                 ' prints 5
    Debug.Print DatePart("ww", MyDate)                ' prints 31

End Sub

DateDiff()

DateDiff() returns a Long representing the number of time intervals between two specified dates.

Syntax

DateDiff ( interval, date1, date2  [, firstdayofweek] [, firstweekofyear] )

• interval can be any of the intervals defined in the DatePart() function
• date1 and date2 are the two dates you want to use in the calculation
• firstdayofweek and firstweekofyear are optional. Refer to DatePart() function for explanations

Examples

Sub DateDiffExamples()

    ' Check to see if 2016 is a leap year.
    Dim NumberOfDays As Long
    NumberOfDays = DateDiff("d", #1/1/2016#, #1/1/2017#)
    
    If NumberOfDays = 366 Then
        Debug.Print "2016 is a leap year."              'This will output.
    End If
           
    ' Number of seconds in a day
    Dim StartTime As Date
    Dim EndTime As Date
    StartTime = TimeSerial(0, 0, 0)
    EndTime = TimeSerial(24, 0, 0)
    Debug.Print DateDiff("s", StartTime, EndTime)       'prints 86400

End Sub

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DateAdd()

DateAdd() returns a Date to which a specified date or time interval has been added.

Syntax

DateAdd ( interval, number, date  ) 

• interval can be any of the intervals defined in the DatePart() function
• number Numeric expression that is the number of intervals you want to add. It can be positive (to get dates in the future) or negative (to get dates in the past).
• date is a Date or literal representing date to which the interval is added

Examples :

Sub DateAddExamples()

    Dim Sample As Date
    'Create sample date and time of 2016-07-28 12:34:56
    Sample = DateSerial(2016, 7, 28) + TimeSerial(12, 34, 56)
    
    ' Date 5 months previously (prints 2016-02-28):
    Debug.Print Format$(DateAdd("m", -5, Sample), "yyyy-mm-dd")
    
    ' Date 10 months previously (prints 2015-09-28):
    Debug.Print Format$(DateAdd("m", -10, Sample), "yyyy-mm-dd")
    
    ' Date in 8 months (prints 2017-03-28):
    Debug.Print Format$(DateAdd("m", 8, Sample), "yyyy-mm-dd")

    ' Date/Time 18 hours previously (prints 2016-07-27 18:34:56):
    Debug.Print Format$(DateAdd("h", -18, Sample), "yyyy-mm-dd hh:nn:ss")
    
    ' Date/Time in 36 hours (prints 2016-07-30 00:34:56):
    Debug.Print Format$(DateAdd("h", 36, Sample), "yyyy-mm-dd hh:nn:ss")

End Sub

CDate()

CDate() converts something from any datatype to a Date datatype

Sub CDateExamples()

    Dim sample As Date

    ' Converts a String representing a date and time to a Date
    sample = CDate("September 11, 2001 12:34")
    Debug.Print Format$(sample, "yyyy-mm-dd hh:nn:ss")      ' prints 2001-09-11 12:34:00
    
    ' Converts a String containing a date to a Date
    sample = CDate("September 11, 2001")
    Debug.Print Format$(sample, "yyyy-mm-dd hh:nn:ss")      ' prints 2001-09-11 00:00:00

    ' Converts a String containing a time to a Date
    sample = CDate("12:34:56")
    Debug.Print Hour(sample)                        ' prints 12
    Debug.Print Minute(sample)                      ' prints 34
    Debug.Print Second(sample)                      ' prints 56
    
    ' Find the 10000th day from the epoch date of 1899-12-31
    sample = CDate(10000)
    Debug.Print Format$(sample, "yyyy-mm-dd")       ' prints 1927-05-18
    
End Sub

Note that VBA also has a loosely typed CVDate() that functions in the same way as the CDate() function other than returning a date typed Variant instead of a strongly typed Date. The CDate() version should be preferred when passing to a Date parameter or assigning to a Date variable, and the CVDate() version should be preferred when when passing to a Variant parameter or assigning to a Variant variable. This avoids implicit type casting.

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DateSerial()

DateSerial() function is used to create a date. It returns a Date for a specified year, month, and day.

Syntax:

DateSerial ( year, month, day ) 

With year, month and day arguments being valid Integers (Year from 100 to 9999, Month from 1 to 12, Day from 1 to 31).

Examples

Sub DateSerialExamples()

    ' Build a specific date
    Dim sample As Date
    sample = DateSerial(2001, 9, 11)
    Debug.Print Format$(sample, "yyyy-mm-dd")                   ' prints 2001-09-11
    
    ' Find the first day of the month for a date.
    sample = DateSerial(Year(sample), Month(sample), 1)
    Debug.Print Format$(sample, "yyyy-mm-dd")                   ' prints 2001-09-11
    
    ' Find the last day of the previous month.
    sample = DateSerial(Year(sample), Month(sample), 1) - 1
    Debug.Print Format$(sample, "yyyy-mm-dd")                   ' prints 2001-09-11
    
End Sub

Note that DateSerial() will accept "invalid" dates and calculate a valid date from it. This can be used creatively for good:

Positive Example

Sub GoodDateSerialExample()

    'Calculate 45 days from today
    Dim today As Date
    today = DateSerial (2001, 9, 11)
    Dim futureDate As Date
    futureDate = DateSerial(Year(today), Month(today), Day(today) + 45)
    Debug.Print Format$(futureDate, "yyyy-mm-dd")            'prints 2009-10-26

End Sub

However, it is more likely to cause grief when attempting to create a date from unvalidated user input:

Negative Example

Sub BadDateSerialExample()

    'Allow user to enter unvalidate date information
    Dim myYear As Long
    myYear = InputBox("Enter Year")                                         
            'Assume user enters 2009
    Dim myMonth As Long
    myMonth = InputBox("Enter Month")                                       
            'Assume user enters 2
    Dim myDay As Long
    myDay = InputBox("Enter Day")                                           
            'Assume user enters 31
    Debug.Print Format$(DateSerial(myYear, myMonth, myDay), "yyyy-mm-dd")   
            'prints  2009-03-03

End Sub