Last week, I got a haircut. Nothing exciting there… many people do that on a typical day.

Sometimes there are very interesting personal finance lessons hiding in the most mundane activities. This was one such case.

I noticed that place I get my haircut, Supercuts was running a promotion: 4 haircuts for $50 via a pre-paid card. I like easy math, so I’ll happily report that comes out to $12.50 a haircut.

The normal price of a haircut: $15.95.

I’ve probably lost about 80% of the readers who did some other quick math: it saves less than $3.50 per haircut.

That doesn’t seem like much, but let’s imagine that I haircut once a month (usually I go longer than that). At ~$16 it is going to cost me $192 a year for those 12 haircuts. By buying the pre-paid cards, it is going to me $150. It’s the exact same service for $42 less.

If you do the math, the savings is 20%. I don’t know of a legitimate investment that will guarantee you a 20% return.

I’ve been thinking about buying up a bunch, since they don’t expire. However, I need your help to know how many to buy. When does it stop becoming worthwhile to buy these cards? For example, if I were buy enough cards for 10 years, that’s tying up a lot of money up-front, which maybe could be better used than saving me 20%.

Let me know in the comments.