The maximum amount your S corp can contribute to your 401(k) as the employer contribution is 25% of your W-2 compensation.
If you were under age 50 in 2017, your maximum employee elective deferral is $18,000 or your available W-2 compensation after subtracting any taxes withheld, whichever is less. (Your total of elective deferral, tax withholding, Social Security tax and Medicare tax cannot exceed your compensation.) However, your election to make an elective deferral was required to have been made by December 31, 2017. Under Department of Labor regulations, the deposit of your elective deferral should have been made by January 15, 2018.
