Sub AddFormulasToComments()
Application.ScreenUpdating = False
Dim CommentRange As Range, TargetCell As Range
'skip over errors caused by trying to delete comments in cells with no comments
On Error Resume Next
'If the whole worksheet is selected, limit action to the used range.
If Selection.Address = Cells.Address Then
  Set CommentRange = Range(ActiveSheet.UsedRange.Address)
Else
  Set CommentRange = Range(Selection.Address)
End If
'If the cell contains a formula, turn it into a comment.
For Each TargetCell In CommentRange
  With TargetCell
    'check whether the cell has a formula
    If Left(.Formula, 1) = "=" Then
      'delete any existing comment
      .Comment.Delete
      'add a new comment
      .AddComment
      'copy the formula into the comment box
      .Comment.Text Text:=.Formula
      'display the comment
      .Comment.Visible = True
    End If
  End With
Next
MsgBox "  To print the comments, choose" & vbCrLf & " File|Page Setup|Sheet|Comments," & vbCrLf & "then choose the required print option.", vbOKOnly
Application.ScreenUpdating = True
End Sub