Don't understand your question. Cap amount?
Self Employment tax (Scheduled SE) is automatically generated if a person has $400 or more of net profit from self-employment. You pay 15.3% SE tax on 92.35% of your Net Profit greater than $400. The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire. You do get to take off the 50% ER portion of the SE tax as an adjustment on 1040 Schedule 1 line 27. The SE tax is already included in your tax due or reduced your refund. It is on the 1040 Schedule 4 line 57 which goes to 1040 line 14. The SE tax is in addition to your regular income tax on the net profit.
If you also have W2 income, you have to break out the Social Security and Medicare taxes. Only the Social Security part maxes out. Turbo Tax does it automatically for you.
The SE tax includes what you already paid in from your W2s so your schedule SE tax will only be the difference up to the max amount of $7,960.80 for social security. The max income for social security for 2018 is $128,400 between W2 wages and the schedule C Net Profit.
Medicare is 2.9% (both er & ee parts) of all wages & schedule C profit - no max.
