Excel VBA: How to Extend a Range Given a Current Selection

You mean like this?

SYNTAX

ExpandRange [Range], [Number of Col on left], [Number of Rows on Top], [Number of Col on right], [Number of Rows down]

Sub Sample()    Debug.Print ExpandRange(Range("B5"), 1, 1, 1, 1)            '<~~ $A$4:$C$6    Debug.Print ExpandRange(Range("A1"), 1, 1, 1, 1)            '<~~ Error    Debug.Print ExpandRange(Range("XFD4"), 1, 1, 1, 1)          '<~~ Error    Debug.Print ExpandRange(Range("XFD1048576"), 1, 1, 1, 1)    '<~~ Error    Debug.Print ExpandRange(Range("E5"), 1, 1, 1, 1)            '<~~ $D$4:$F$6End SubFunction ExpandRange(rng As Range, lft As Long, tp As Long, _rt As Long, dwn As Long) As String    If rng.Column - lft < 1 Or _       rng.Row - tp < 1 Or _       rng.Column + rt > ActiveSheet.Columns.Count Or _       rng.Row + dwn > ActiveSheet.Rows.Count Then        ExpandRange = "Error"        Exit Function    End If    ExpandRange = Range(rng.Offset(-1 * tp, -1 * lft).Address & ":" & _                        rng.Offset(dwn, rt).Address).AddressEnd Function

Here is the simple code that I use to resize an existing selection.

Selection.Resize(Selection.Rows.Count + 5, Selection.Columns.Count + 50).Select

This will add 5 to the row count and 50 to the column count. Adapt to suit your needs.

You can use Application.WorksheetFunction.Offset() which is richer than VBA's Offset and does everything required by the question.
I think it does what Siddharth Rout ExpandRange does, without the need of a UDF.