How Arizona withholds on a bonus
Arizona is unusual: instead of a supplemental rate set by the state, withholding on all wages, bonuses included, is the percentage the employee elected on Form A-4, which offers 0.5%, 1%, 1.5%, 2%, 2.5%, 3% and 3.5% of gross taxable wages, with 2% applied if no form is filed. The calculator uses 2.5%, Arizona's flat income tax rate and the election that lands closest to the actual liability for most single filers. On a $10,000 bonus that is $250 of Arizona withholding, alongside $2,200 federal, $620 Social Security and $145 Medicare, leaving $6,785.
An employee who chose 3.5% on the A-4 sees $350 withheld from the same bonus; one who chose 1% sees $100. Because Arizona's tax is a flat 2.5% after a standard deduction, any election above 2.5% over-withholds and returns as a refund. There are no local income taxes in Arizona, so the state line is the whole state-and-local picture.
What the withholding means for your Arizona return
Arizona's tax on a bonus is 2.5% of it, less nothing, because the standard deduction has usually been used up by regular salary. So 2.5% withholding on a bonus settles close to even, and the refund or balance due on a bonus comes almost entirely from the federal side: a $60,000 single filer's marginal federal rate is 12% to 22%, against the 22% withheld. The Arizona paycheck calculator shows the marginal rates for any salary and the A-4 percentage that matches them. Arizona's Form A-4 sets the percentage withheld on a bonus as on every other paycheck; an employee who wants more or less withheld from a bonus changes the A-4 election, since there is no separate bonus rate to choose.