Answer by Alex34758 for Aligning controls on both left and right side in a stack panel in WPF

User @pasx is right. You should use DockPanel and dock the RadioButton to the left side, and your StackPanel with the label to the right side.

<DockPanel><DockPanel         DockPanel.Dock="Top"        LastChildFill="False"><RadioButton             DockPanel.Dock="Left"            Content="_Programs"            IsChecked="{Binding Path=ProgramBanksSelected}"            IsEnabled="{Binding Path=ProgramsEnabled}"            Margin="8" /><StackPanel            DockPanel.Dock="Right"><Label                 Content="Master"                Height="28"                Name="MasterFileStatus"                VerticalContentAlignment="Center"/></StackPanel></DockPanel>    ...