the employee shall be entitled to a special refund of the amount, if any, by which the employee tax imposed by section 3101 with respect to such wages and deducted therefrom (whether or not paid) exceeds the employee tax with respect to the amount specified in (a) through (h) of this subdivision for the calendar year in question. Employee tax imposed by section 3101 with respect to tips reported by an employee to his employer and collected by the employer from funds turned over by the employee to the employer (see section 3102(c)) shall be treated, for purposes of this paragraph, as employee tax deducted from wages received by the employee. If the employee is required to file an income tax return for such calendar year (or for his last taxable year beginning in such calendar year) he may obtain the benefit of the special refund only by claiming credit as provided in § 1.31-2 of this chapter (Income Tax Regulations).
Example. Employee A rendered services to X during 1973 for which he was paid compensation at the monthly rate of $650 which was taxable under the Railroad Retirement Tax Act. A was paid $550 by X in January 1973 which was earned and deemed received in December 1972 and $650 in January of 1974 which was earned and deemed received in December of 1973. A also earned and received wages in 1973 from employer Y, which were subject to the employee tax under the Federal Insurance Contributions Act, in the amount of $6,000. A paid hospital insurance tax on $13,800 ($7,800 compensation from X including $650 earned and deemed received in December 1973 but paid in January 1974 and not including $550 paid in January 1973 but earned and deemed received in December 1972, $6,000 compensation from Y) received or deemed received or earned in 1973. For purposes of the hospital insurance tax imposed by section 3101(b), these amounts are all wages received from an employer in 1973. Therefore, A is entitled to a special refund for 1973 under section 6413(c) and this section of $30 (1.0% * $13,800 - 1.0% * $10,800).
26 C.F.R. §31.6413(c)-1