Public Sub New()
        InitializeComponent()
        Dim mask As String = "9999.99"
        MaskedTextBox1.Mask = mask
        MaskedTextBox2.Mask = mask
        MaskedTextBox3.Mask = mask
    End Sub
 
    Private Sub MaskedTextBox_TextChanged(ByVal sender As System.Object, ByVal _
      e As System.EventArgs) Handles MaskedTextBox1.TextChanged, _
      MaskedTextBox2.TextChanged, MaskedTextBox3.TextChanged
        Label1.Text = GetTextCalculation.ToString("n")
    End Sub
 
    Private Function GetTextCalculation() As Double
        Dim value1, value2, value3 As Double
        If Not Double.TryParse(MaskedTextBox1.Text, value1) Then Return 0
        If Not Double.TryParse(MaskedTextBox2.Text, value2) Then Return 0
        If Not Double.TryParse(MaskedTextBox3.Text, value3) Then Return 0
        Return value1 + value2 + value3
    End Function