Starbucks, in an effort to bolster its lagging afternoon traffic, has started a new promotion. Starting Tuesday, any customer that buys a Starbucks drink in the morning can use the receipt later that same day to buy any grande (medium) iced coffee drink for $2, about half of its usual price.

Before you add this to your daily routine, though, think about this: a grande (16 oz.) Iced Peppermint White Chocolate Mocha at SBux has 400 calories. If you add this to your weekday routine without cutting back elsewhere on your eating, you could pick up as much as 30 pounds in a year. Ouch! Ask your barrista for suggestions on how you can satisfy your afternoon caffeine jones without outgrowing your wardrobe. Or be prepared to blow your savings with Jenny Craig.

If you're interested in saving even more, though, you might try making your own Starbucks-like drink at home. While you prepare it, enjoy Lewis Black's take on the chain's market penetration.