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AddDays Method

DateTime.AddDays Method

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

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

public DateTime AddDays(
	double value
)

Parameters

value
Type: System.Double

A number of whole and fractional days. The value 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 the number of days represented by value.

ExceptionCondition
ArgumentOutOfRangeException

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

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

The fractional part of value is the fractional part of a day. For example, 4.5 is equivalent to 4 days, 12 hours, 0 minutes, 0 seconds, 0 milliseconds, and 0 ticks.

The value parameter is rounded to the nearest millisecond.

The AddDays method takes into account leap years and the number of days in a month when performing date arithmetic.

The following example uses the AddDays method to determine the day of the week 36 days after the current date.

using System;

class Class1
{
	static void Main()
	{
		DateTime today = DateTime.Now;
		DateTime answer = today.AddDays(36);
        Console.WriteLine("Today: {0:dddd}", today);
        Console.WriteLine("36 days from today: {0:dddd}", answer);
	}
}
// The example displays output like the following: 
//       Today: Wednesday 
//       36 days from today: Thursday

.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
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