I don't worry about the # of exemptions. I use the withhold a fixed dollar amount in employee express to increase the withholding to what I want it to be, for federal and state. So in other words, I have enough exemptions claimed so that I would be under-withholding without the extra fixed dollar amount.
I play with the fixed dollar amount at the beginning of the year until I'm sure I have it so that I am withholding annually at least as much as my total tax liability was the prior year.
Then around September or October, I look at it again to guestimate if I need to have a little more withheld.
I usually end up paying a little with my return, which is fine, I just don't want to be getting a refund. I know as long as I have paid in 100% of my total tax from the prior year, I won't be getting a penalty (which I'm not allowed to have.)
GGAL