W-9 income isn't initially withheld; payees must report and pay taxes themselves ... subject to backup withholding, the current flat rate set by the IRS is 28%. So, to calculate how much you ...

The IRS Tax Withholding Estimator is a free and essential tool for U.S. taxpayers who want to make sure the right amount is withheld from their paychecks.

Bonuses are considered part of your wages, tips and other compensation, and are taxed accordingly. Employers calculate withholding taxes on bonuses using the percentage or aggregate method.