How an Alabama paycheck works
Alabama does something no other state's payroll does: it lets you deduct the federal income tax withheld from your pay before working out the state tax. The two lines on your payslip are therefore linked, and a raise that pushes you into a higher federal bracket also enlarges your Alabama deduction, which softens the state side of the increase.
Federal income tax withholding
Federal withholding annualises the wage, subtracts the standard deduction for 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 blank: one job, no spouse income, no other income, no extra withholding. In Alabama this figure does double duty, because it is also one of the state deductions.
Social Security and Medicare
Social Security takes a flat rate on wages up to an annual ceiling that moves each year. Medicare applies to every dollar, and above a fixed threshold the employer withholds the Additional Medicare tax on the excess. Neither is deductible against Alabama tax; only the federal income tax is.
Four deductions, then three rate steps
The state formula takes the annual wage and removes four things in turn: the standard deduction for your filing status, the federal income tax withheld for the year, a personal exemption, and an amount for each dependant. What is left goes through three narrow rate steps, and because those steps are so narrow almost any full-time salary is taxed at the top rate on its last dollar.
The standard deduction is not a single figure. It is at its full amount up to a threshold, then falls by a fixed step for each increment of income above it, "or part thereof" as the booklet puts it, until it reaches a floor. Married employees get the largest starting amount and lose it fastest.
The dependent exemption has two cliffs
Unlike most states, Alabama's per-dependant amount is not constant. It is one figure up to a gross income threshold, a smaller one above it, and smaller again above a second threshold. These are genuine cliffs, not tapers: a single dollar of extra salary at the wrong point cuts the exemption for every dependant at once and raises the state tax by more than the dollar earned. The calculator reproduces the cliffs because the state's own formula has them.
Local income tax
Several Alabama cities and counties charge an occupational tax on wages earned there, Birmingham among them. Rates depend on where the work is performed and are not included below, so add your local rate if your workplace has one.
What the employer pays on top
The employer matches Social Security and Medicare and pays federal unemployment tax at its net rate. Alabama unemployment insurance is an employer contribution at an experience-rated percentage on a state wage base. There is no employee-side state levy.
What this calculator assumes
The figure models a salaried employee paid evenly across the year with a standard Form W-4 and Form A-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 change the federal figure and therefore the Alabama one too.
- Extra withholding requested on either certificate, and the W-4 Step 2 and Step 4 adjustments.
- Bonuses and other supplemental wages.
- Local occupational taxes and employer-side Alabama unemployment insurance.
- The married filing separately column, which has its own deduction schedule; single is modelled here.
Withholding versus your final tax bill
Withholding is a prepayment. On the Alabama return the federal deduction is your actual federal liability rather than what was withheld, so the two rarely match exactly, and the standard deduction is recomputed from your Alabama adjusted gross income. Expect a small difference either way.