This method does not change the value of this DateTime object. Instead, a new DateTime object is returned 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.