四百多可能是payroll tax。

低于一万二不用交收入税，但是social security/medicare tax还是要交的，这个叫做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/?