Mark on Form W-4 that you are Single. You can use the IRS Tax Withholding Estimator to estimate any extra amount you should withhold. Divide the amount among your remaining pay periods for the current year and note that amount to Form W-4 Line 4(c). It will add to your Federal withholdings on your W-2. If you have too much withheld, it will be refunded on your tax return.
