Employees with too much or too little tax withheld from their paycheck can give their employer a new Form W-4.  Mid-year is a good time to make adjustments if needed.   The IRS Withholding Calculator  can be used to determine the number of allowances to claim.  If you are self-employed, Form 1040ES should be used to remit quarterly estimated tax payments and can also be used to determine the amount of tax to remit.