Mobile Workforce State Income Tax Simplification Act of 2012

Mobile Workforce State Income Tax Simplification Act of 2012 - Prohibits the wages or other remuneration earned by an employee who performs employment duties in more than one state from being subject to income tax in any state other than: (1) the state of the employee's residence, and (2) the state within which the employee is present and performing employment duties for more than 30 days during the calendar year. Exempts employers from withholding of tax and information reporting requirements for employees not subject to income tax under this Act. Allows an employer, for purposes of determining penalties related to employer withholding or reporting requirements, to rely on an employee's annual determination of the time such employee will spend working in a state in the absence of fraud or collusion by such employee.

Exempts from the definition of "employee" for purposes of this Act professional athletes, professional entertainers, and public figures who are persons of prominence who perform services for wages or other remuneration on a per-event basis.

Makes this Act effective on January 1 of the 2nd year that begins after the enactment of this Act. Renders this Act inapplicable to any tax obligation that accrues before the effective date of this Act.