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DateTime.AddMonths Method (Int32)


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Returns a new DateTime that adds the specified number of months to the value of this instance.

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

public DateTime AddMonths(
	int months


Type: System.Int32

A number of months. The months parameter can be negative or positive.

Return Value

Type: System.DateTime

An object whose value is the sum of the date and time represented by this instance and months.

Exception Condition

The resulting DateTime is less than MinValue or greater than MaxValue.


months is less than -120,000 or greater than 120,000.

This method does not change the value of this DateTime object. Instead, it returns a new DateTime object whose value is the result of this operation.

The AddMonths method calculates the resulting month and year, taking into account leap years and the number of days in a month, then adjusts the day part of the resulting DateTime object. If the resulting day is not a valid day in the resulting month, the last valid day of the resulting month is used. For example, March 31st + 1 month = April 30th, and March 31st - 1 month = February 28 for a non-leap year and February 29 for a leap year.

The time-of-day part of the resulting DateTime object remains the same as this instance.

The following example adds between zero and fifteen months to the last day of December, 2015. In this case, the AddMonths method returns the date of the last day of each month, and successfully handles leap years.

using System;

public class Example
   public static void Main()
      var dat = new DateTime(2015, 12, 31);
      for (int ctr = 0; ctr <= 15; ctr++)

// The example displays the following output:
//       12/31/2015
//       1/31/2016
//       2/29/2016
//       3/31/2016
//       4/30/2016
//       5/31/2016
//       6/30/2016
//       7/31/2016
//       8/31/2016
//       9/30/2016
//       10/31/2016
//       11/30/2016
//       12/31/2016
//       1/31/2017
//       2/28/2017
//       3/31/2017

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
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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