Find Last Cell with Data and Drag that Formula Down

Hello,

I am trying to find the last cell in column B which is in Row 10000+ and copy the formula down to the last cell based on Column A's last row. Here is what I'm starting with:

Dim lastRow, dragRange as Long
lastRow = Range("B2").End(xlDown).Row
dragRange = Range("A2").End(xlDown).Row

I know how to drag a formula down based on a fixed cell such as:

Dim dragRange As Long
dragRange = Range("B2").End(xlDown).Row
Range("A2").AutoFill Destination:=Range("A2:A" & dragRange), Type:=xlFillValues

But, I don't know how to drag a formula down when the cell is not fixed. I don't want to AutoFill any rows above, just B10000 (or whatever the row is at the time) and below. Any help would be greatly appreciated.

Thank you in advance for your time.