Add Serial Numbers in new column up to last row based on next column

[VB_Gizmo2018]

Dear Community,
I am returning back to VBA after a very long break and have managed to forgotten the code to run a macro that adds serial numbers on the left hand side of a blank column from start of the data up to the last row based on a column with last row data which can vary in legth

from

Column A	Column B	Column C	Column D
	RG4500	1.2	Phase 3
	CIV550	33.3	Phase 2
	RG4400	6.1	Phase 2
	CV990	0	Phase 2
	DC20122	6	Phase 2
	CV990		Phase 2
	CIV550		Phase 2
	RG4500

<colgroup><col width="64" style="width: 48pt;" span="4">
<tbody>






















































</tbody>

to

Column A	Column B	Column C	Column D
1	RG4500	1.2	Phase 3
2	CIV550	33.3	Phase 2
3	RG4400	6.1	Phase 2
4	CV990	0	Phase 2
5	DC20122	6	Phase 2
6	CV990		Phase 2
7	CIV550		Phase 2
8	RG4500

<colgroup><col width="64" style="width: 48pt;" span="4">
<tbody>






















































</tbody>

I remember I have to define lastrow variable based on say column B and run the sequence up to 8th row in above example but thats about it.

I didnt find anything similar in existing threads to created this thread
thanks in advance

 

[Scott T]

try

Sub serialnum()
Dim lr As Long
lr = Cells(Rows.Count, 2).End(xlUp).Row
a = 1
For x = 2 To lr 'assumes row headers in row 1 and numbers should start in row 2
    Cells(x, 1) = a
    a = a + 1
Next x
End Sub

 

[Fluff]

Another option

Sub AddValues()
Range("A2").Value = 1
Range("A2").AutoFill Range("A2", Range("B" & Rows.Count).End(xlUp).Offset(, -1)), xlFillSeries
End Sub