It depends- it is not necessarily a mistake on behalf of your employer. If you haven't updated your W-4 with your employer recently, I would suggest starting there. Check your paystubs, and if the withholding doesn't increase to a level of your satisfaction, then direct your employer to withhold a specific amount per pay. Based on this year, ask for $120 additional withholding per pay if you get paid bi-weekly, or $60 per pay if you are paid weekly.
