Two rules on the same page, and everybody merges them
Almost every W-4 guide on the internet contains a version of "only fill in the form for your highest paying job". Half of that is right and the half that is wrong is expensive.
The form itself says two separate things:
- Step 2(c): "If there are only two jobs total, you may check this box.Do the same on Form W-4 for the other job." That is both forms.
- Steps 3 to 4(b): "Complete Steps 3-4(b) on Form W-4 for only ONE of these jobs. Leave those steps blank for the other jobs." That is one form, and it should be the highest paying one.
Collapse those into a single instruction and the Step 2(c) box quietly falls off the second W-4. The tables then treat each job as though it were the only one, each gets a full standard deduction's worth of untaxed pay, and the household under-withholds every payday for a year. The bill arrives in April, often with an underpayment penalty attached, and nothing on any payslip flagged it.
Ticking it on only one of the two is the worst outcome of the three, because the calculation splits the deduction and the brackets in half on one job and not the other.
Step 4(c) is per paycheck, and the form shouts it
"Extra withholding. Enter any additional tax you want withheld each pay period." The words "pay period" are printed in bold on the form because of how often this goes wrong.
Somebody who owed $5,200 last year, and would like that covered this time, writes 5,200 in the box. On biweekly pay that is $5,200 taken twenty-six times. Payroll does exactly what the form says and nobody queries it, because the number came from the employee.
Work out the annual figure, divide by the number of paychecks in your year, and enter that. Fifty-two weekly, twenty-six biweekly, twenty-four twice-monthly, twelve monthly.
What Step 3 is worth in 2026
$2,200 for each qualifying child under 17, and $500 for each other dependent. The child figure went up from $2,000, so a W-4 sitting in a payroll file from last year is now claiming slightly too little and over-withholding.
Step 3 only works as printed while total income is at or under $200,000, or $400,000 filing jointly. Above that the credit tapers by $50 for every $1,000 over, and the face of the form stops giving the right answer. The estimator at irs.gov/W4App handles the taper; this tool holds Step 3 at zero rather than claiming something you would have to repay.
No W-4 is not a neutral choice
If you never handed one in, and that applies to anybody hired since 2019 who slipped through, your employer withholds as a single filer with no adjustments. That is the harshest treatment available: no dependents, no deductions, no allowance for a joint return. It is worth asking payroll what they hold rather than assuming something sensible was defaulted in.
Why this looks nothing like a British tax code
The two systems answer the same question and hand the job to opposite people. In the UK, HMRC issues a tax code straight to your employer, the employee never touches it, and a problem is something you have to get the government to correct. In the US you fill the W-4 in yourself and hand it over, so a problem is usually your own form and the fix is handing in a new one, which you can do at any time.
That difference is why the failure modes are so different. British withholding goes wrong through a code nobody explained. American withholding goes wrong through a form nobody read properly. Canada uses Form TD1, federal and provincial, and Australia a tax file number declaration, and both of those sit on the employee's side of the desk too.
Common questions
Do I check the Step 2(c) box on both jobs or just one?
Both. The form says it in plain words: "If there are only two jobs total, you may check this box. Do the same on Form W-4 for the other job." Ticking it on only one of the two is worse than ticking neither, because the withholding tables split the standard deduction and the brackets across both jobs and that only balances when both forms agree.
So why does everyone say to fill in only the higher paying job?
Because there are two different rules on the same page and they get collapsed into one. Steps 3 to 4(b), the dependents and deductions, do go on one form only, and the form says to use the highest paying job for them. The Step 2(c) checkbox is separate and goes on both. Guides that merge the two drop the box off the second W-4, which under-withholds all year.
Is Step 4(c) per paycheck or per year?
Per pay period, and the form prints "pay period" in bold for exactly this reason. Somebody wanting a $5,200 cushion over the year who writes 5200 in that box on biweekly pay gets $5,200 taken twenty-six times. Work out the annual figure you want, divide by the number of paychecks, and put that in instead.
How much is each dependent worth on Step 3?
$2,200 for each qualifying child under age 17 and $500 for each other dependent, for 2026. The child figure rose from $2,000, so a W-4 filled in on last year’s numbers now claims slightly too little. It only applies if total income is $200,000 or less, or $400,000 or less filing jointly.
What happens if I never handed in a W-4 at all?
Your employer withholds as a single filer with no adjustments, which is the harshest treatment on the table. That applies to anyone hired since 2019 who never submitted one. If you cannot remember filling one in, it is worth asking payroll rather than assuming a sensible default was applied.
What is the difference between this and a UK tax code?
Who fills it in. In the UK, HMRC issues a tax code directly to your employer and you never touch it, so a problem is something you have to get the government to correct. In the US you complete the W-4 yourself and hand it to your employer, so a problem is usually a form you filled in wrongly and can fix by handing in a new one. Canada uses Form TD1 and Australia a TFN declaration, both of which the employee also fills in.
Should I aim for a big refund?
A large refund means you lent the IRS money for a year at no interest. Withholding close to your actual liability leaves that money in your pay instead. The opposite error costs more though: under-withholding can bring an underpayment penalty as well as the bill, so if you are going to be out either way, being slightly over is the cheaper direction.