It's amazing how much simple carelessness can cost. In my case, it was six weeks.

I'm a budget nerd (among many other varieties of nerd). I learned the hard way that personal finance requires more than spending whatever feels right, cashing your paycheck and hoping the numbers balance.

On my laptop, I've got a giant spreadsheet outlining our monthly expenses, our debts, our savings, our assets and pretty much all of our hopes and dreams. A couple times a month I'll pop it open and start fiddling with the numbers.

What if we added this expense? What if we paid off this debt? I'm constantly looking for ways to trim a little fat.

You'd think after a few years of doing this, there wouldn't be much fat left to be trimmed. My wife would probably argue there's a good amount of muscle and bone that's been hacked at over the years too, and I might cut out a vital organ if she'd let me. One sore thumb sticking out has always been our cell-phone bill. I hate cell phones, but she (probably correctly) insists they are essential for modern living. She has one, and that doubles as our only phone.

We signed up for it in 2006 and have been with the same carrier, on the same plan, ever since. At the time, I didn't know a whole lot about cell phones and there were a lot of horror stories on the news about people going over their monthly allotment of minutes and being saddled with huge bills.

I picked out a plan based on my fear of overages, combined with my compulsion to never buy the cheapest option offered me out of fear of looking, well, cheap,

We've hummed along on that plan since then, never paying a cent in overages. As I looked at a half-year's worth of bills last week, I realized why.

We'd never used more than one-fifth of the total we're allowed. Their cheapest plan could cover our usage twice over.

And what's more, I could change plans right there on their web site with a few clicks, cutting the cell-phone bill almost in half.

I did some quick calculations. Difference between cheapest option and what we'd been paying, times the amount of time we'd had the phones, equals about three times my takehome pay every two weeks.

I worked a full-time job for six weeks in the last few years, just to pay the phone company for something I never used.

I'm sure I'm not the only one out there who makes these kinds of mistakes, and I know I'm among the minority when I actually look for them.

In these tough economic times, Americans are being forced to account for decades of overspending and dependence on unnecessary credit. A lot of us would find our tough times get a little less tough with a little less carelessness and a lot more thought.