When utilizing the tax calculator I would consider increasing your income to reflect a higher commissions. If you commissions are always changing this could be causing your to have inaccurate calculations. Another item to take into account is as an hourly employee you can to keep in mind any OT. One thing to note is if you are using an average of your hourly rate and commissions you can add additional taxes to be withheld on your W-4 to account for any fluctuations. You should also review these calculations quarterly to have a more accurate understanding on where your pay is.
