eg, $90K in California? back of the envelope
28% $87,850 to $183,250 Federal Rate
15.30%* Social Security, self employed
8.8% State-Level taxes
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~ 52% Aggregate tax rate (excluding 9% sales tax average).
This is not an average rate, nor does it include the provision of the healthcare mandate. In any event, this is meant to be illustrative only, and the marginal and average dynamics play out differently at higher rates (for a variety of reasons, including tax-sheltering and regressive taxes on payroll and sale/consumption taxes).