DateTime Subtract

In a C# program, one DateTime can be subtracted from another. This returns the difference in time between the 2 dates.

For example, the difference between December 25 and January 1 in the year 2008 is seven days. The Subtract() method can be used for this purpose.

Example

We use the Subtract method with one argument on the DateTime struct instance. We must subtract the smaller date from the larger date.

using System;

class Program
{
    static void Main()
    {
        // Create DateTime instances for December 25 and January 1.
        // ... Then compute the difference with Subtract.
        // ... Write the result.
        DateTime christmas = new DateTime(2008, 12, 25);
        DateTime newYears = new DateTime(2009, 1, 1);
        TimeSpan span = newYears.Subtract(christmas);
        Console.WriteLine(span);
        Console.WriteLine("{0} days", span.TotalDays);
    }
}
7.00:00:00
7 days

Discussion

Each DateTime struct stores a ticks field—this is a long type representation of the time. When using Subtract, the long fields from the two DateTime instances are simply subtracted.

Summary

Subtract() receives one argument and returns a TimeSpan instance indicating the elapsed time. Typically we subtract a smaller and earlier date from the larger date.