I always make certain my W-2 is withholding the highest amount possible. I like to try to eliminate the possibility of owing the government anything and I enjoy the hefty refund too. I know I would just spend the money if it were in my regular check. I enjoy the extra cushion. With that said, I withhold at the higher single rate with 0 exemption allowances. This withholds the highest amount of tax possible but ensures I get a refund when I file my taxes since I usually don't have any additional income where taxes were not withheld. I hope this helps.