Kentucky Form K-4 vs Federal W-4: What Each One Actually Controls (2026)

Most guides describe the Kentucky K-4 as "the state's version of the W-4." That framing is wrong, and it leads people to fill out the form when they don't need to — or to leave it blank when they should have filed it.

The two forms are not parallel. The federal W-4 is where you fine-tune your federal withholding. The Kentucky K-4 does almost nothing by comparison: it exists to record an exemption from Kentucky withholding, or a request for extra Kentucky withholding. There is no third thing it does.

Before you check any box, know what is actually at stake: the exemption switches off Kentucky's 3.5% flat withholding and nothing else. The K-4 exemption helper walks you through the four boxes in plain language and shows the dollar difference on your own wages — federal tax, FICA, and local occupational tax all keep coming out either way.

What the Kentucky K-4 Actually Is

The current form is K-4, Kentucky's Withholding Certificate, revision 42A804 (K-4)(11-2023), published by the Kentucky Department of Revenue. Printed on it is one line of tax math, four checkboxes, one dollar field, and a signature.

That's it. The four checkboxes are exemptions:

1. You don't expect any Kentucky income tax liability this year
2. You qualify for the Fort Campbell exemption (you work on the base but live in another state)
3. You qualify for the nonresident military spouse exemption
4. You work in Kentucky but live in a reciprocal state

Below them is a single line — "Additional withholding per pay period under agreement with employer $____" — and then you sign under penalty of perjury.

There is no allowance count, no dependent worksheet, no filing status, and no place to enter a spouse's income. Kentucky removed all of that when it moved to a flat tax. Any guide that tells you to "claim 1 or 2 allowances on your K-4" is describing a form that no longer exists.

Why that myth is so persistent

Search for the Kentucky K-4 and one of the top results is still 42A804 (11-13) — the 2013 form. It has an allowance worksheet, and it carries the line "Failure to file this form with your employer will result in withholding tax deductions from your wages at the maximum rate."

Both of those were true in 2013. Neither is true now. Check the revision code in the bottom corner of any K-4 you're handed: if it isn't (11-2023) or later, it's the wrong form.

Most Employees Never Need to File One

This is the part almost nobody states plainly, so here it is in the Department of Revenue's own words, from the employer instructions on page 2 of the form:

"Form K-4 is only required to document that an employee has requested an exemption from withholding OR to document that an employee has requested additional withholding in excess of the amounts calculated using the formula or tables. If neither situation applies, then an employer is not required to maintain Form K-4."

If you are an ordinary Kentucky employee who wants ordinary Kentucky withholding, there is nothing for you to do. Your employer runs the statutory formula — flat rate, one standard deduction, everybody — and that is the correct answer. Filing a blank K-4 changes nothing.

You only file a K-4 to say "stop withholding, I'm exempt" or "withhold more than the formula says."

What the Federal W-4 Does

The federal W-4 (Employee's Withholding Certificate) is the opposite: it's where nearly all of the tuning happens. The IRS redesigned it in 2020 and removed allowances there too, replacing them with concrete dollar amounts and checkboxes across five steps — filing status, multiple jobs, dependent credits, other income and deductions, and extra withholding.

Federal tax is progressive, from 10% to 37%, and depends on your filing status and credits, so the form needs that detail to land close to your actual bill.

Side-by-Side Comparison

How Kentucky Withholding Is Actually Computed

Since the K-4 carries no personal detail, the formula is the same for every employee who hasn't claimed an exemption:

1. Annualize your wages for the pay period
2. Subtract the standard deduction — $3,360 for 2026, the same figure regardless of filing status or dependents
3. Apply the flat rate of 3.5% to what's left
4. Divide back down to the pay period, and add any amount from the K-4's additional-withholding line

One caution about the form itself: the (11-2023) revision still prints "a flat 4% rate with a standard deduction allowance of $3,160" at the top, because that was correct for 2024. For 2026 the rate is 3.5% and the deduction is $3,360. Your employer's payroll system uses the current figures; the paper form simply hasn't been reprinted. Don't do the math off the numbers on the page.

Our Kentucky paycheck calculator runs this formula alongside federal withholding, FICA, and your local occupational tax.

The Trap: "Exempt" Doesn't Mean Tax-Free

Checking a K-4 exemption box stops state withholding. It does not stop:

• Federal income tax — that's the W-4's job
• Social Security and Medicare — 7.65% combined, and no state form touches it
• Your local occupational tax — Louisville, Lexington, Covington and most other Kentucky cities levy their own payroll tax on wages earned in the city, and it is completely unaffected by your K-4

That last one surprises people every year. A Fort Campbell exemption or a reciprocal-state exemption zeroes your Kentucky state tax and leaves the local tax fully in place, because local occupational tax follows where the work happens, not where you're domiciled. You can see the size of that gap in the Kentucky occupational tax rate table.

When to Revisit Your K-4

Because the form only handles exemptions and extra withholding, the triggers are narrower than for a W-4:

• ✅ The exemption you claimed no longer applies. Box 1 exemptions expire on February 15 of the following year — if you still qualify, you have to file a new K-4. A Fort Campbell exemption must be revoked within 10 days of moving to Kentucky.
• ✅ Your circumstances changed a military or reciprocity answer — your spouse leaves the service, you stop living at the same address, or you move out of a reciprocal state.
• ✅ You owed Kentucky money at filing time and want to close the gap with a fixed amount per paycheck. That's the additional-withholding line.
• ❌ Marriage, a new baby, or a home purchase on their own change nothing about your Kentucky withholding. They matter a great deal on your W-4. Kentucky's flat rate and single standard deduction don't respond to any of them.

Common Mistakes

Mistake 1: Assuming the W-4 controls Kentucky withholding

Your federal W-4 has no effect on Kentucky state tax withholding, and the K-4 has no effect on federal. They are separate forms controlling separate taxes.

Mistake 2: Claiming exempt when you don't qualify

Box 1 is only for people who expect zero Kentucky income tax liability — realistically, income below the filing threshold for your family size. The thresholds are tied to the federal poverty level and are restated in the instructions on the current form each year. Checking the box because your refund was large last year is not a qualifying reason, and it produces a bill plus penalties at filing time.

Mistake 3: Filling out an obsolete form

If the K-4 in front of you asks how many allowances you're claiming, it's a pre-2019 form. Fill it out and you've documented a request that current payroll rules can't act on. Get revision (11-2023) or later.

Mistake 4: Expecting a blank K-4 to maximize withholding

Not filing a K-4 doesn't trigger "maximum rate" withholding — that was the old form's rule. Today, no K-4 simply means the standard formula. If you want more withheld, you have to write a dollar amount on the additional-withholding line.

Frequently Asked Questions

How many allowances should I claim on my Kentucky K-4?

None — the current K-4 has no allowance field. Kentucky eliminated withholding allowances when it adopted a flat tax with a single standard deduction. If you're looking at a form with an allowance worksheet, it's the 2013 revision or earlier and is no longer in use.

Can I submit my K-4 electronically?

That depends on your employer's payroll system. Many HRIS platforms accept an electronic equivalent. If yours doesn't, print, sign, and hand it to payroll — the signature is made under penalty of perjury, so it has to be yours.

What happens if I don't file a K-4?

Nothing unusual. Your employer withholds Kentucky tax using the standard formula (flat 3.5% on wages above the $3,360 standard deduction). The old form's "maximum rate" penalty language no longer applies, and employers aren't required to keep a K-4 on file for employees who aren't claiming an exemption or extra withholding.

Is the K-4 the same as the federal W-4?

No, and they aren't even similar in scope. The K-4 controls Kentucky's flat 3.5% withholding and offers only an exemption or an extra-withholding amount. The W-4 controls federal withholding across the 10%–37% brackets and collects filing status, dependents, and other income.

I moved to Kentucky from another state mid-year. Do I need a K-4?

Only if you had previously claimed an exemption that no longer applies. If you were exempt as a Fort Campbell nonresident or a reciprocal-state resident, you must file a new K-4 removing that claim — within 10 days, in the Fort Campbell case. If you were never exempt, your employer will withhold Kentucky tax on your Kentucky wages automatically.

Does claiming exempt on my K-4 stop my city's occupational tax?

No. Local occupational taxes are levied by cities and counties on wages earned within their boundaries and are administered separately from state withholding. A K-4 exemption leaves them entirely untouched.