How do I center a window onscreen in C#?

Use Form.CenterToScreen() method.

1. Using the Property window

   Select form → go to property window → select "start position" → select whatever the place you want.

   

2. Programmatically

   Form form1 = new Form(); form1.StartPosition = FormStartPosition.CenterScreen; form1.ShowDialog();

   Note: Do not directly call Form.CenterToScreen() from your code. Read here.

A single line:

this.Location = new Point((Screen.PrimaryScreen.WorkingArea.Width - this.Width) / 2,
                          (Screen.PrimaryScreen.WorkingArea.Height - this.Height) / 2);

In Windows Forms:

this.StartPosition = FormStartPosition.CenterScreen;

In WPF:

this.WindowStartupLocation = WindowStartupLocation.CenterScreen;

That's all you have to do...