What is Schedule SE?
Schedule SE calculates the self-employment tax — the Social Security and Medicare you owe on business profit, since no employer is splitting it with you.
How it works
You take your net profit from Schedule C, multiply by 92.35%, and apply 15.3% (12.4% Social Security up to the wage base, plus 2.9% Medicare). Then you get to deduct half of that tax on your 1040, which softens the blow.
A quick example
What people get wrong
This is the tax that shocks first-year freelancers. It's on top of income tax and starts at just $400 of net earnings — budget for the full 15.3%, not just your income-tax bracket.