It's been a long week. I'm tired. Worn out. I'm looking forward to the weekend. But before I sign off for the weekend I thought about having a little bit of educational fun on a Friday morning.

Regular readers know I'm something of a quant. I like to run the numbers, do the analysis. One kind of analysis I'm particularly fond of is the Monte Carlo simulation. The Monte Carlo simulation is just about the best way, short of a reliable crystal ball, to foretell the future. I enjoy running these simulations on various portfolio decisions to see how they will affect my retirement.

The thing about retirement and Monte Carlo simulations, however, is you need to tell it how far into the future to project. That's where the fun starts today. Northwestern Mutual has a Longevity Game on their site. Think you're living a healthy life? Go use their longevity calculator to find out.

Start out by plugging in your age, weight, height and sex. From there it gets into things like family medical history and your own lifestyle. As you answer each question your longevity meter is updated in real time, letting you see the impact of each factor as you go along.

I'm typically pretty conservative in my own analyses. I've been using age 100 for my calculations. Looks like I'm being about 10% too conservative. That's not a bad margin of error.

Go ahead and play around with it a while. And be honest, the stress from lying and feeling guilty about it is bad for your longevity.

Northwester Mutual's Longevity Game