Math Formula for Money Line Bets?

I understand the conversion from a moneyline to a percentage, and was wondering if anybody ever uses some sort of formula to determine a teams percent chance of winning the game.  I have been doing this for hockey and have quit posting, but will say that when I have the time to do this that I have hit at a decent rate.  I was combining both teams home and road records to come up with a percent change of them winning.  Are there other ideas?