With metrocards, or anything you purchase on a regular basis that you can sit down and calculate a near exact cost of (cable bill, monthly memberships, etc), buying in bulk is a no-brainer. However, things you consume or use up, like gas or food, likely end up costing more when bought in bulk.

This happens if you don’t have a system for how you plan on using what you bought over an extended period. Instead of buying one Twinkie a day, you might think you’re saving $20 buying a big monthly supply (monthly supply being 31 Twinkies, for example). Without any form of control or restriction placed on the Twinkies, it’s likely you will now just end up eating more than one Twinkie per day. You might finish the Twinkies in a week instead of a month, and then probably either get sick of them and quit buying them for a week or two, and then resuming the cycle, or resuming it right away. Food isn’t the only thing we can abuse…

With a full tank in the car, I’m much more likely to speed or drive aggressively. With multiple bags of cat food in storage, I would probably take out scoops without caring much about losing any bits of food. I.e., some bits fell on the floor, or I put too much and need to throw out the old bits.

This also happens with money. If you have $100 in your bank account, you’re much less likely to charge small purchases, and become very vigilant about what you’re buying. With $3,500 in your bank account, this self monitoring is inhibited because suddenly, the loss is insignificant relative to how much you have in the bank. This is illogical. Saving $1 is saving $1,whether you have $2 in the bank or $2,000.

This doesn’t mean you shouldn’t buy in bulk. Buying in bulk is an excellent way to save money, but also requires that you micromanage your supply.