INDEX Function Works In Cell But Not In VBA

I've been working on a payroll program for my small biz. I'm close to done BUT...

When I use the Index Match function in a cell it works great. However I need to copy it down a column to work for pay periods going forward. When I copy it down of course it puts zeros or N/A.

Columns:

Gross Fed FICA Medicare State Net
F G H I J K

Gross is user input. FICA Medicare State and Net are simply calculated on the sheet. But to get Fed Income tax I use the Index Match function and it works perfectly. The rows increment properly with each new user input.

Code:

=INDEX(SingleWH!C$6:M$140,MATCH(G7,SingleWH!A$6:A$140,1),MATCH(E$1,SingleWH!C$4:M$4,0))

This is the code in Column F. You can see where it uses the result in Column G to look for a value in sheets("SingleWH").

My question: Fed Income tax is dependent on what the Gross is in order to look up the tables with the Index Match function. How do I get the result of the function into column G? Can I increment up Column G and ignore the zeros that dragging the function down G creates?