Arizona is the one state with no withholding formula
Every other state tells employers how to compute the state tax to take from a paycheck. Arizona does not. Arizona law makes withholding a percentage that you pick, from a short list on Form A-4, applied to your gross taxable wages. Your employer does not calculate anything; it applies the percentage you chose.
That leaves nothing to reproduce. So the Arizona line on this page is not what an employer would withhold — it is the Arizona income tax you owe for the year. The federal lines above it are still ordinary withholding. Read the state line as a tax bill and the federal lines as prepayments, and the two are not the same kind of number.
How the Arizona figure is worked out
Arizona charges a single flat rate on taxable income, the same rate whatever you earn and whatever your filing status. Taxable income here is your wage less the standard deduction for your filing status. That is exactly the calculation Arizona's own estimated tax worksheet asks a taxpayer to do for the year, so the page follows the state's published method rather than inventing one.
Arizona conforms its standard deduction to the federal one, and it sets three amounts: one for a single filer or someone married filing separately, a larger one for a head of household, and the largest for a married couple filing jointly. Choosing married or head of household therefore does change the Arizona figure, through the deduction rather than through the rate.
Federal income tax withholding
Federal withholding annualises the wage, subtracts the standard deduction that matches the filing status on Form W-4 Step 1, applies the graduated schedule for that status, and deducts the dependent credit from Step 3. This page models a W-4 with Steps 2 and 4 left blank: one job, no spouse income, no other income, no extra withholding. Above the income limit for the status, the dependent credit tapers by a set amount for every thousand dollars of excess rather than disappearing at a cliff.
Social Security and Medicare
Social Security applies a flat rate to wages up to an annual ceiling that is re-indexed each year, so it stops partway through the year for a high earner. Medicare applies to every dollar, and above a fixed wage threshold the employer withholds the Additional Medicare tax on the excess, with no employer match and no regard for filing status.
Form A-4 and what it means for your paycheck
Form A-4 offers a handful of percentages to choose between, and the default until you file it is one of the lower ones. You may also elect zero, if you expect to owe no Arizona tax for the year, and that election has to be renewed each year or it lapses. Because the choice is yours, two people on the same salary in the same town can have very different amounts taken from their paychecks and still owe exactly the same tax.
The practical consequence is that Arizona is the easiest state in which to under-withhold by accident. Pick a percentage well below your effective rate and the shortfall arrives with your return. Compare the figure on this page with what your payslip actually shows and you will see immediately which way you are leaning.
Why the deduction here is the previous year's
Arizona's department of revenue publishes each year's inflation-adjusted standard deduction well after the year begins. Its own estimated tax booklet for the current year tells taxpayers to use the previous year's standard deduction when working out what they will owe. This page does the same thing, for the same reason, so the figure matches the method the state itself hands to taxpayers. When the adjusted amount is published, the figure moves slightly.
One more piece of context. The standard deduction Arizona currently uses matched the federal amount because the governor directed the department to apply it, while the legislature had not yet passed the conformity bill that would settle it in law. That is a live question in Arizona rather than a settled one, and it is worth knowing if you are planning around the exact number.
What Arizona does not tax
There is no Arizona county or city income tax, so there is no local line on this page and no equivalent of the residence question that decides local tax in states like Maryland or Indiana. There is also no employee-side state levy: no disability insurance, no paid family leave premium. The Arizona line is the whole of the state's claim on your wages.
What the employer pays on top
The employer matches Social Security and Medicare and pays federal unemployment tax at its net rate. Arizona unemployment insurance is charged to the employer at a rate set from its own claims record on a state wage base, so it is left out.
What this calculator assumes
The figure models a salaried employee paid evenly across the year with a standard Form W-4 and no pre-tax deductions. It leaves out:
- Pre-tax contributions such as a 401(k), health premiums, HSA or flexible spending accounts, which reduce the wages subject to income tax and often to FICA.
- Extra withholding requested on the federal certificate, and the W-4 Step 2 and Step 4 adjustments.
- Itemised deductions, which replace the standard deduction for some filers, and Arizona's subtractions and tax credits.
- Bonuses and other supplemental wages.
- Employer-side state unemployment insurance, which is priced per employer, and any federal unemployment credit reduction.
- Employees outside the normal Social Security system, such as some public-sector staff and certain visa holders.
Liability versus what lands in your bank account
Because the state line here is a liability rather than a withheld amount, the take-home figure answers the question "what is this salary worth after tax in Arizona" rather than "what will my payslip say". For most people those are close, because most people pick a percentage near their effective rate. If you elected zero, or a percentage far from it, your payslip will differ and the difference settles on your return.