Making Excel automatically subtract

are you talking about a basic subtraction formula?

=sum(a2-e2)

Assume the toal figure is in cell F1
Assume the list of clients is from A2 to A1000 with their orders in the range B2:B1000
A B
1 NAME WIGETS
2 Bill 6
3 Tom 8
4 Fred 9

The formula in, say F3 could be:

=$F$1-SUM(B2:B1000)

(BTW a simple subtraction does not require the SUM function =A1-B2 is sufficient)

Sounds like you're looking for a rudimentary inventory control process and there are many ways to skin that cat. One approach would be to list items sold by name and quantity in one sheet, and you can subtotal those rows/transactions and know how many of each item you've sold in a given period (sheet). Then in another sheet you your "current inventory count" which should reflect how much of each item you have at a given point in time. Then you have a third sheet which is the "running totals" - that's where you subtract [current inventory total] minus [current sold count] as DL suggests.

At some point you have to copy/paste special/values the "running totals" and overwrite the "current totals." You can do that manually as needed, or you could spend a ton of time and money writing macros to automate some of the updates. You can probably find some cheap or free-ware templates out there too. Google "free Excel inventory" or the like and see what you get.

It can, but you will need to enter another formula and column for your totals. Example:
Column B would be for added inventory, Column C dor removed or deleted inventory, Column E for total. Formula in E would be =E2+B3-C3. The
cell E2 would be the beginning quantity. THis will track added and used inventory.