Why Is Illinois Tax the Same on Every Paycheck?

Why is Illinois tax the same on every paycheck? Because the state charges one flat rate, 4.95 percent, with no brackets at all. Whether you earn $30,000 or $200,000, the state takes the same share, and unlike the federal line it never steps up as the year goes on.

Flat means genuinely flat

Most states step you through brackets, so your effective rate climbs as income rises. Illinois does not, and the figures make the point better than the description does.

• $30,000: $1,485 of Illinois tax, 4.95% of gross
• $52,000: $2,574, 4.95%
• $75,000: $3,712.50, 4.95%
• $120,000: $5,940, 4.95%
• $200,000: $9,900, 4.95%

Five incomes spanning nearly seven times the pay, and the same percentage every time.

This is also why the Illinois figure on your pay stub scales so predictably. Double your gross for a period, because of a bonus or a heavy overtime week, and the Illinois line doubles with it. Nothing tips into a higher band, because there is no higher band to tip into, which is the opposite of how the federal line behaves on the same check.

What the federal line is doing meanwhile

The contrast is the whole reason the Illinois line looks so still. Across those same five incomes, federal tax as a share of pay goes:

• $30,000: 4.73%
• $52,000: 7.81%
• $75,000: 10.23%
• $120,000: 14.64%
• $200,000: 18.37%

Illinois paycheck deductions on $52,000

On $52,000, paid biweekly, filing single, with no pretax deductions:

Line	Per paycheck	Rate	Per year
Gross pay	$2,000.00	—	$52,000.00
Federal income tax	−$156.15	varies with your W-4	−$4,059.90
Social Security	−$124.00	6.2%	−$3,224.00
Medicare	−$29.00	1.45%	−$754.00
Illinois income tax	−$99.00	4.95% flat	−$2,574.00
Local income tax	$0.00	none	$0.00
Take-home	$1,591.85	79.6% of gross	$41,388.10

The Illinois line is the smallest of the four and the only one you can work out in your head. Four dollars ninety-five for every hundred, every time.

The two things that do move it

A flat rate does not mean a fixed dollar amount. Two things change the base the rate is applied to, and both are worth knowing about.

Withholding allowances

Illinois has its own allowance system, separate from the federal W-4, claimed on a state form. Each allowance reduces the amount the rate is charged on, and on a biweekly check the effect is steady:

• 0 allowances: $99.00 a period, $2,574 a year
• 1 allowance: $93.43, $2,429 a year
• 2 allowances: $87.86, $2,284
• 3 allowances: $82.29, $2,140
• 4 allowances: $76.73, $1,995

Each one is worth about $5.57 a period, or $145 a year, and the value is identical whether it is your first or your fourth. That is the flat rate showing through again. It is also why an Illinois allowance form filled in once at hire and never revisited is a quiet, recurring cost.

Pretax deductions

Retirement contributions, health premiums and an HSA come out before the rate is applied, so they reduce the Illinois figure as well as the federal one. The saving is exactly 4.95 percent of whatever you divert.

• $100 to retirement: Illinois tax falls from $99.00 to $94.05, a saving of exactly $4.95
• $200: $89.10, saving $9.90
• $400: $79.20, saving $19.80

Precisely proportional, which no bracketed state can offer. In Illinois you can price a retirement contribution against the state line without a calculator at all.

What does not move it

Filing status. Single or married, the Illinois figure on $52,000 is $99.00 either way. Only the federal line responds, which is why an Illinois couple comparing paychecks after a marriage often finds one number changed and the other did not.

Nor does the calendar. Because there are no brackets to climb into, the Illinois line looks the same in December as it did in January. Social Security is the only deduction on the pay stub that can stop mid-year, and that only affects high earners past the wage base.

What a flat rate means in practice

A flat rate is not automatically better or worse than brackets, it is differently shaped, and where you sit on the income scale decides which you would prefer.

Someone on $30,000 pays 4.95 percent to Illinois while their federal effective rate is 4.73 percent, so the state takes slightly more of their pay than Washington does. Someone on $200,000 pays the same 4.95 percent against a federal effective rate of 18.37 percent, so the state line is a small fraction of their bill. In a bracketed state those two positions would be much further apart. Whether that is fair is a genuine policy argument with people on both sides of it, and Illinois has had the argument publicly more than once.

What is not arguable is the practical consequence: Illinois is unusually easy to plan around. You can price a raise, a bonus or a retirement contribution against the state line with mental arithmetic, which is not true anywhere with brackets.

Against a state with no income tax at all

On $52,000, the Illinois take-home is $41,388. In Texas, where there is no state income tax, the same salary leaves $43,962.

The gap is $2,574 a year, which is the Illinois tax figure exactly, since the two states are otherwise identical on federal tax and FICA. About a hundred dollars a paycheck. Real money, and smaller than the difference a change in housing costs would make in either direction, which is worth keeping in proportion when the comparison comes up.

One thing worth checking separately is local tax. Illinois cities do not levy an income tax the way some Ohio or Michigan cities do, so there is usually no fifth line, but it is worth confirming against your own pay stub rather than assuming.

The calculator below breaks your own check into the same lines, including the allowance effect, and the take-home pay by state calculator puts the flat 4.95 percent beside states that use brackets so you can see where it wins and where it does not.

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