Why doesn't Marketplace Health Insurance Premiums go on Schedule C for a self-employed person? If it went on Schedule C it would lower the profit and thereby lower the Self-Employed Tax calculation along with SEP contribution.
Adding it to Schedule 1 line 17 makes the Self-Employed person pay more SE taxes and have higher contributions into SEP (not a bad thing).
The reason the Self-employed health deduction is not on Schedule C, but on Schedule 1 of form 1040 is because it is a tax break authorized by tax laws, and not an ordinary and necessary expense of your business.
How are health insurance premiums not an ordinary/necessary cost of doing business for myself? You have to have health insurance.
If I was an employee, the company I work for would be allowed to deduct the cost of premiums. I am my own employee from janitor to CEO that is supported by my business revenue.
If you were an employee your W2 would reflect the payment for your health insurance and you would still pay social security and medicare tax on any employee contribution amounts that you made. Moving the deduction away from schedule C means that the deduction is still there and keeps you from paying income tax on the health insurance amount but makes you pay self-employment tax on the amount paid for health insurance (which is the social security and medicare).