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AddMonths Method

DateTime.AddMonths Method

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.


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. 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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
© 2015 Microsoft