With net profit of $26,624, the deductible portion of SE taxes being $0, a regular elective deferral of $18,500 and a catch-up elective deferral of $6,000, your maximum permissible employer contribution is :
($26,624 - $0 - $18,500) / 2 = $4,062
This is due to the section 415(c)(1)(B) limit which stipulates that your employer contribution cannot be more than 100% of income which is your net profit minus the sum of the deductible portion of SE taxes plus your regular elective deferrals and employer contributions:
$26,624 - ($0 + $18,500 + $4,062) = $4,062
TurboTax will calculate this automatically when you mark the Maximize box for an individual 401(k).
