四百多可能是payroll tax。

低於一萬二不用交收入稅，但是social security/medicare tax還是要交的，這個叫做payroll tax。

In most cases, the federal payroll tax rate is about 15.3%, with the employee covering 7.65% and the employer covering 7.65%. If you’re self-employed—as a sole proprietor or business owner—you’re responsible for the full 15.3%, usually referred to as self-employment tax.

https://www.forbes.com/advisor/business/payroll-tax-rates/?