Bonus Tax Calculator (Percentage vs Aggregate)

A bonus is not taxed under a separate tax schedule; it is ordinary compensation. What differs is the withholding mechanics, because the IRS classifies bonuses as supplemental wages in Publication 15 (Circular E). Employers may use the flat percentage method, which withholds 22 percent of any supplemental payment up to 1,000,000 dollars in a calendar year and 37 percent on the portion above that, or the aggregate method, which adds the bonus to the most recent regular wage payment and withholds as if that combined amount were normal pay. This calculator models both, then layers on the payroll taxes that apply regardless of method: Social Security at 6.2 percent up to the wage base of 168,600 dollars used here, Medicare at 1.45 percent with no ceiling, and the 0.9 percent Additional Medicare Tax once combined wages pass 200,000 dollars. The practical consequence is that withholding and liability rarely match. A worker whose marginal bracket is 12 percent is over-withheld by roughly ten points under the flat method and recovers the difference at filing; a worker in the 32 or 35 percent bracket is under-withheld and owes at filing. Effective total bite on a bonus commonly lands between 30 and 45 percent once a state rate of 0 to 13.3 percent is added. Two caveats matter: the Social Security component depends on year-to-date wages already earned, which this tool approximates from annual salary rather than an actual payroll ledger, and states apply their own supplemental rules that may not mirror the federal flat rate.

Supplemental wage withholding grew out of the wartime pay-as-you-go system created by the Current Tax Payment Act of 1943, which made employers responsible for collecting income tax at the source rather than leaving workers to settle a lump sum each March. Once withholding was continuous, the Treasury had to decide how irregular payments such as commissions, back pay, and year-end bonuses should be handled, since a percentage-of-wage table designed for steady paychecks badly distorted a one-time payment. Regulations issued under Internal Revenue Code section 3402 eventually authorized employers to treat such payments separately using a flat rate, which is the ancestor of today's percentage method. The flat rate itself has moved with statutory tax cuts. It stood at 20 percent for much of the 1990s, was raised to 28 percent, then set at 25 percent by the Jobs and Growth Tax Relief Reconciliation Act of 2003, tied to the third-lowest bracket. The American Jobs Creation Act of 2004 added the higher tier for supplemental wages above 1,000,000 dollars, pegged to the top marginal rate. The Tax Cuts and Jobs Act of 2017 lowered the standard supplemental rate to 22 percent and the upper tier to 37 percent effective in 2018, the figures still in force. Social Security and Medicare components trace to the Social Security Act of 1935 and the Medicare amendments of 1965.