DateTime.Subtract Method (DateTime)
Subtracts the specified date and time from this instance.
Assembly: mscorlib (in mscorlib.dll)
Parameters
 value

Type:
System.DateTime
The date and time value to subtract.
Return Value
Type: System.TimeSpanA time interval that is equal to the date and time represented by this instance minus the date and time represented by value.
Exception  Condition 

ArgumentOutOfRangeException 
The Subtract(DateTime) method determines the difference between two dates. To subtract a time interval from the current instance, call the Subtract(TimeSpan) method. To subtract a particular time interval from the current instance, call the method that adds that time interval to the current date, and supply a negative value as the method argument. For example, to subtract two months from the current date, call the AddMonths(Int32) method with a value of 2.
If the date and time of the current instance is earlier than value, the method returns a TimeSpan object that represents a negative time span. That is, the value of all of its nonzero properties (such as Days or Ticks) is negative.
TheSubtract(DateTime) method does not consider the value of the Kind property of the two DateTime values when performing the subtraction. Before subtracting DateTime objects, ensure that the objects represent times in the same time zone. Otherwise, the result will include the difference between time zones.
Note 

The DateTimeOffset.Subtract(DateTimeOffset) method does consider the difference between time zones when performing the subtraction. 
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1