Read the offer as a transaction
Write down how many items must be purchased and the total payable. Check whether different products qualify, whether sizes must match and whether a membership price is involved. Then compare with buying the quantity already on your list. This keeps the promotion from deciding your needs for you.
Suppose one hypothetical item costs $4 and three cost $10. The three pack costs about $3.33 each, but a household needing only two would otherwise spend $8. Accepting the offer requires $2 more today. Whether that is useful depends on the third item's role.
Give the extra item a destination
If the third item will replace a definite purchase next week, the extra quantity may be sensible. If it will be forgotten, expire or encourage unnecessary consumption, the lower unit price has not produced the expected benefit. Use past consumption rather than an optimistic estimate prompted by the discount.
Mixed offers deserve particular attention. A cheaper qualifying item added to an expensive pair may change the actual saving. Calculate the combination you will buy rather than relying on the maximum saving mentioned in the advertisement. Include any required accessories or preparation costs when the products differ.
Keep the weekly limit intact
A promotion can reduce longer term cost while making this week's basket unaffordable. Check what the extra cash would displace before buying ahead. It is reasonable to decline a good unit price when the money is needed for a more immediate commitment.
After using the offer, note whether the additional quantity replaced a later purchase. That simple observation provides evidence for the next promotion. If the extra remains unused, do not repeat the purchase just because the offer returns. A sale is a chance to buy planned consumption more cheaply; it should not become a recurring reason to expand the household's stock of things nobody had originally intended to buy.
For products sold in varying sizes, compare the total contents of the qualifying packs rather than assuming every item is equivalent.
