No withholding is required on wages paid while a certificate in the prescribed form is in effect in which the employee certifies that he or she had no income tax liability for the preceding taxable year and expects none for the current year. The regulations coordinate this exemption with the allowance rules: the exempt certificate expires on 15 February of the following year unless renewed, after which the employer withholds as single with no adjustments (or on the last valid non-exempt certificate), and the exemption does not apply to social security and Medicare taxes.
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