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DateAdd Function

Returns a Date value containing a date and time value to which a specified time interval has been added.

Public Overloads Function DateAdd( _
   ByVal Interval As DateInterval, _
   ByVal Number As Double, _
   ByVal DateValue As DateTime _
) As DateTime

-or-

Public Overloads Function DateAdd( _
   ByVal Interval As String, _
   ByVal Number As Double, _
   ByVal DateValue As Object _
) As DateTime

Parameters

Interval
Required. DateInterval enumeration value or String expression representing the time interval you want to add.
Number
Required. Double. Floating-point expression representing the number of intervals you want to add. Number can be positive (to get date/time values in the future) or negative (to get date/time values in the past). It can contain a fractional part when Interval specifies hours, minutes, or seconds. For other values of Interval, any fractional part of Number is ignored.
DateValue
Required. Date. An expression representing the date and time to which the interval is to be added. DateValue itself is not changed in the calling program.

Settings

The Interval argument can have one of the following settings.

Enumeration value String Unit of time interval to add
DateInterval.Day d Day; truncated to integral value
DateInterval.DayOfYear y Day; truncated to integral value
DateInterval.Hour h Hour; rounded to nearest millisecond
DateInterval.Minute n Minute; rounded to nearest millisecond
DateInterval.Month m Month; truncated to integral value
DateInterval.Quarter q Quarter; truncated to integral value
DateInterval.Second s Second; rounded to nearest millisecond
DateInterval.Weekday w Day; truncated to integral value
DateInterval.WeekOfYear ww Week; truncated to integral value
DateInterval.Year yyyy Year; truncated to integral value

Exceptions/Errors

Exception type Error number Condition
InvalidCastException 13 DateValue is not coercible to Date.
ArgumentException 5 Interval is invalid.
ArgumentOutOfRangeException 9 Calculated date is before 00:00:00 on January 1 of the year 1, or later than 23:59:59 on December 31, 9999.

Remarks

You can use the DateAdd function to add or subtract a specified time interval from a date. For example, you can calculate a date 30 days from today or a time 45 minutes before now.

To add days to DateValue, you can use DateInterval.Day, DateInterval.DayOfYear, or DateInterval.Weekday. These are treated as equivalent because DayOfYear and Weekday are not meaningful time intervals.

The DateAdd function never returns an invalid date. If necessary, the day part of the resulting date is adjusted downward to the last day of the resulting month in the resulting year. The following example adds one month to January 31:

Dim NextMonth As Date = DateAdd(DateInterval.Month, 1, #1/31/1995#)

In this example, DateAdd returns #2/28/1995#, not #2/31/1995#. If DateValue is #1/31/1996#, it returns #2/29/1996# because 1996 is a leap year.

If any argument has an invalid value, an ArgumentException error occurs. If the calculated date is earlier than 00:00:00 on January 1 of the year 1, or later than 23:59:59 on December 31, 9999, an ArgumentOutOfRangeException error occurs. If the DateValue argument has a value that cannot be coerced to a valid Date value, an InvalidCastException error occurs.

Note   DateAdd uses the current calendar setting from the CurrentCulture property of the CultureInfo class in the System.Globalization namespace. The default CurrentCulture values are determined by Control Panel settings.

Since every Date value is supported by a DateTime structure, its methods give you additional options in adding time intervals. For example, you can add a fractional number of days, rounded to the nearest millisecond, to a Date variable as follows:

Dim NextTime As Date = Now        ' Current date and time.
NextTime = NextTime.AddDays(3.4)  ' Increment by 3 2/5 days.

Example

This example takes a date and, using the DateAdd function, displays a corresponding date a specified number of months in the future.

Dim Msg, Number, StartDate As String   'Declare variables.
Dim Months As Double
Dim SecondDate As Date
Dim IntervalType As DateInterval
IntervalType = DateInterval.Month   ' Specifies months as interval.
StartDate = InputBox("Enter a date")
SecondDate = CDate(StartDate)
Number = InputBox("Enter number of months to add")
Months = Val(Number)
Msg = "New date: " & DateAdd(IntervalType, Months, SecondDate)
MsgBox (Msg)

Requirements

Namespace: Microsoft.VisualBasic

Module: DateAndTime

Assembly: Microsoft Visual Basic .NET Runtime (in Microsoft.VisualBasic.dll)

See Also

DateDiff Function | DatePart Function | Day Function | Format Function | Now Property | Weekday Function | Year Function | Date Data Type | System Namespace | System.Globalization Namespace | DateTime Structure | ArgumentException Class | ArgumentOutOfRangeException Class | InvalidCastException Class | CultureInfo Class

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