Recently married. W-4 question

The total tax you and your wife will owe using married filing joint status will probably be less than if you had not married and filed separate returns as single, and it is all but certain that your tax will be less than using married filing separate. However, there is no way to tell what benefit, if any, you will garner without more information. It is possible your combined incomes will push you into a higher tax bracket while your withholding remains in a lower bracket. Thus the increase in net pay could result in you owing tax when you file your returns for 2015 simply because you had less withheld.