Under section 404(e)(4), notwithstanding the provisions of subparagraphs (1) and (2) of this paragraph, the limitations on the amount deductible for the taxable year of the employer with respect to contributions on behalf of a self-employed individual shall not be less than the lesser of $750 or 100 percent of the earned income derived by such individual for such taxable year from the trade or business with respect to which the plan is established. If such individual receives in any taxable year earned income with respect to which deductions are allowable to two or more employers, 100 percent of such earned income shall be taken into account for purposes of the limitations determined under this subparagraph. This subparagraph does not apply to any taxable year beginning after December 31, 1975, to any employee whose adjusted gross income for that taxable year is greater than $15,000. In applying the preceding sentence, the adjusted gross income of an employee for a taxable year is determined separately for each individual, without regard to any community property laws, and without regard to the deduction allowable under section 404(a).
26 C.F.R. §1.404(e)-1A