DateTime.AddSeconds() Method in C#

The DateTime.AddSeconds() method in C# is used to add the specified number of seconds to the value of this instance. This returns a new DateTime object without modifying the original DateTime instance.

Syntax

Following is the syntax −

public DateTime AddSeconds(double sec);

Parameters

sec − A double value representing the number of seconds to be added. If you want to subtract seconds, then set a negative value. The value can include fractional seconds.

Return Value

This method returns a new DateTime object that represents the date and time after adding the specified seconds. The original DateTime instance remains unchanged.

Using AddSeconds() to Add Seconds

Example

using System;

public class Demo {
   public static void Main() {
      DateTime d1 = new DateTime(2019, 10, 25, 6, 20, 40);
      DateTime d2 = d1.AddSeconds(25);
      
      Console.WriteLine("Initial DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d1);
      Console.WriteLine("New DateTime (After adding seconds) = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d2);
   }
}

The output of the above code is −

Initial DateTime = 25 October 2019, 06:20:40 
New DateTime (After adding seconds) = 25 October 2019, 06:21:05 

Using AddSeconds() to Subtract Seconds

Example

using System;

public class Demo {
   public static void Main() {
      DateTime d1 = new DateTime(2019, 10, 25, 6, 20, 40);
      DateTime d2 = d1.AddSeconds(-10);
      
      Console.WriteLine("Initial DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d1);
      Console.WriteLine("New DateTime (After subtracting seconds) = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d2);
   }
}

The output of the above code is −

Initial DateTime = 25 October 2019, 06:20:40 
New DateTime (After subtracting seconds) = 25 October 2019, 06:20:30 

Using Fractional Seconds

Example

using System;

public class Demo {
   public static void Main() {
      DateTime d1 = new DateTime(2019, 10, 25, 6, 20, 40, 500);
      DateTime d2 = d1.AddSeconds(2.75);
      
      Console.WriteLine("Initial DateTime = {0:yyyy-MM-dd HH:mm:ss.fff}", d1);
      Console.WriteLine("New DateTime (After adding 2.75 seconds) = {0:yyyy-MM-dd HH:mm:ss.fff}", d2);
   }
}

The output of the above code is −

Initial DateTime = 2019-10-25 06:20:40.500
New DateTime (After adding 2.75 seconds) = 2019-10-25 06:20:43.250

Conclusion

The DateTime.AddSeconds() method provides a convenient way to add or subtract seconds from a DateTime instance. It returns a new DateTime object, preserving immutability, and accepts both positive and negative values including fractional seconds for precise time calculations.