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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)

DateTime AddDays(
	double 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.


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 namespace System;

int main()
   // Calculate what day of the week is 36 days from this instant.
   DateTime today = System::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, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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