How do you center your main window in WPF?

private void CenterWindowOnScreen()
{
    double screenWidth = System.Windows.SystemParameters.PrimaryScreenWidth;
    double screenHeight = System.Windows.SystemParameters.PrimaryScreenHeight;
    double windowWidth = this.Width;
    double windowHeight = this.Height;
    this.Left = (screenWidth / 2) - (windowWidth / 2);
    this.Top = (screenHeight / 2) - (windowHeight / 2);
}

You can use this method to set the window position to the center of your screen.

Well, for startup time, you can set the startup location:

window.WindowStartupLocation = WindowStartupLocation.CenterScreen;

Later, you'll need to query it. The information (at least for the primary screen) is available via SystemParameters.PrimaryScreenWidth/Height.