How a bonus is withheld in Washington
Washington has no income tax on wages and no local income taxes, so the income tax lines on a bonus are federal only: withholding at the flat 22% supplemental rate (or under the aggregate method), Social Security at 6.2% up to the $184,500 wage base, and Medicare at 1.45%. On a $10,000 bonus the percentage method withholds $2,200, $620 and $145, leaving $7,035 before two state premiums that are not income tax: Paid Family and Medical Leave (employee share about 0.66%, $66) and WA Cares (0.58%, $58). Neither is included in the estimate above.
Washington's 7% capital gains tax does not touch a bonus; it applies to investment gains above about $278,000. Under the aggregate method the federal withholding on a $10,000 bonus for a $60,000 earner paid every two weeks is about $2,700 rather than $2,200, and the extra returns at filing.
What the withholding means for your federal return
A single filer on $60,000 has a federal marginal rate of 12% up to $50,400 of taxable income and 22% above it, so a $10,000 bonus is really taxed at about $1,450 against $2,200 withheld, and about $750 returns as part of the refund. A Washington resident who earns a bonus for work in Oregon or Idaho is withheld for that state on it. The Washington paycheck calculator shows the federal marginal rate for any salary. A Washington bonus appears on the W-2 with the state wage boxes blank, and no state income tax return is filed; the only reconciliation is on the federal Form 1040.