In determining the amount deductible, an employer must apply either subdivision (i) of this subparagraph for all employees or subdivision (ii) of this subparagraph for all employees. If contributions paid by an employer in a taxable year to fund such medical benefits under a pension or annuity plan exceed the limitations of this subparagraph but otherwise satisfy the conditions for deduction under section 404, then the excess contributions are carried over and are deductible in succeeding taxable years of the employer which end with or within taxable years of the trust for which it is exempt under section 501(a) in order of time to the extent of the difference between the amount paid and deductible in each succeeding year and the limitation applicable to such year under this subparagraph. For purposes of subdivision (i) of this subparagraph, if the remaining future service of an employee is one year or less, it shall be treated as one year.
26 C.F.R. §1.404(a)-3