VLOOKUP only looks up value from the first column.
For your case, you value (code) is in the second column (B), so you use of
vlookup is not right.
Try to use

=H6-INDEX(Invoice!$A$16:$B$32,MATCH(B6,Invoice!$A$16:$ B$32,0))

--
Best regards,
---
Yongjun CHEN
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"Paula_p" wrote in message
...
Hi,
I have two worksheets, an invoice, and an inventory. What i need is to be
able to deduct quantity sold (from the invoice) from the quantity in stock
(in the inventory). I tried using a vlookup formula to get the product
code
from the invoice and subtract the quantity sold from an amount bought and
recorded in the invetory list. The formula is as follows:
=H6-(VLOOKUP(B6,Invoice!$A$16:$B$32,1,TRUE)). However, this only reduces
the
amount by 3, whether or not the amount sold is 3. Does anyone know what
i'm
doing wrong? Please, any help is appreciated.

Column H - has the anount of goods bought and is available for sale.
Column B - has the unique probuct code.

In the invoice sheet,
Column A - has the quantity sold
Column B - has the code

Thank You.