Self-employment tax is only a Federal tax--it is your contribution to Social Security and Medicare (if you were employed by another company, you would contribute half (7.65% of your wages, up to a limit) and the employer would contribute the other half. When you are self-employed, you pay both halves (although your "company" portion is a deduction against your overall taxable income). States do not charges self-employment tax, although in the case of California, you may be able to opt-in to their state disability program and unemployment.