DateTimeOffset.AddDays Method (Double)


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Returns a new DateTimeOffset object that adds a specified number of whole and fractional days to the value of this instance.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public DateTimeOffset AddDays(
	double days


Type: System.Double

A number of whole and fractional days. The number can be negative or positive.

Return Value

Type: System.DateTimeOffset

An object whose value is the sum of the date and time represented by the current DateTimeOffset object and the number of days represented by days.

Exception Condition

The resulting DateTimeOffset value is less than MinValue.


The resulting DateTimeOffset value is greater than MaxValue.

The fractional part of the days parameter is the fractional part of a day. For example, 4.5 is equivalent to 4 days, 12 hours, 0 minutes, 0 seconds, 0 milliseconds. The days parameter is rounded to the nearest millisecond.


This method returns a new DateTimeOffset object. It does not modify the value of the current object by adding days to its date and time.

Because a DateTimeOffset object does not represent the date and time in a specific time zone, the AddDays method does not consider a particular time zone's adjustment rules when it performs date and time arithmetic.

Converting time intervals of less than a day to a fraction can involve a loss of precision. If this is problematic, you can use the Add method, which enables you to specify more than one kind of time interval in a single method call and eliminates the need to convert time intervals to fractional parts of a day.

The following example uses the AddDays method to list the dates that fall on Monday, the start of the work week, in March 2008.

DateTimeOffset workDay = new DateTimeOffset(2008, 3, 1, 9, 0, 0, 
int month = workDay.Month;
// Start with the first Monday of the month
if (workDay.DayOfWeek != DayOfWeek.Monday)
   if (workDay.DayOfWeek == DayOfWeek.Sunday)
      workDay = workDay.AddDays(1);
      workDay = workDay.AddDays(8 - (int)workDay.DayOfWeek);
Console.WriteLine("Beginning of Work Week In {0:MMMM} {0:yyyy}:", workDay);
// Add one week to the current date 
   Console.WriteLine("   {0:dddd}, {0:MMMM}{0: d}", workDay);
   workDay = workDay.AddDays(7);
} while (workDay.Month == month); 
// The example produces the following output:
//    Beginning of Work Week In March 2008:
//       Monday, March 3
//       Monday, March 10
//       Monday, March 17
//       Monday, March 24
//       Monday, March 31             

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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