Bonus fits into the category of "supplemental wages" which Google suggests has a special 22% tax rate. However that rate also apparently applies to RSUs most of the time.

> Bonus fits into the category of "supplemental wages" which Google suggests has a special 22% tax rate. However that rate also apparently applies to RSUs most of the time.

This 22% tax rate is the default rate applied by your RSU brokerage which often leaves you owing taxes to the IRS. IRS treats RSU at vesting as regular income. For the tax purposes it is same as if you received their equivalent in cash and then used it to purchase the same number company shares [0].

[0] https://www.cordantwealth.com/rsus-tax-saving-and-hedging/

This is a “withholding rate” (how much tax your employer will deduct from your paycheck) not an actual tax rate that you will owe