Calculate difference between two dates from DateTimePicker using C# in Windows Forms Application

Already provided you the complete code. Please check does you have assigned event handler for both the DateTimePicker.

If you have not assigned the go to the property of DateTimePicker and assign ValueChanged event handler for these.

You can also assign using code behind. For this you need to add the below line of code.

public Form1()
{
    InitializeComponent();
    dateTimePicker1.ValueChanged += new EventHandler(dateTimePicker1_ValueChanged);
    dateTimePicker2.ValueChanged += new EventHandler(dateTimePicker1_ValueChanged);
}