How does federal paycheck tax withholding work?

Gross pay vs. net pay

Your salary is quoted in gross pay, the full amount before anything is taken out. Net pay, or take-home pay, is what actually lands in your bank account after deductions. The gap between the two is usually a surprise the first time you see a real pay stub, and almost all of it is tax.

Three things come out of a typical federal paycheck: federal income tax withholding, FICA taxes (Social Security and Medicare), and any pretax deductions you elected, such as a 401(k) contribution or health-insurance premium. Only the first is something you actively control through a form; the rest follow fixed rules or your own benefit choices.

• Gross pay: your stated wage or salary, before deductions
• Federal income tax withheld: a prepayment toward your annual tax bill, set by your W-4
• FICA: Social Security 6.2% and Medicare 1.45%, automatic and not adjustable
• Net pay: what's left after all of the above (plus any state tax, which this guide sets aside)

The W-4: how you tell your employer what to withhold

Withholding is your employer's best guess at what you'll owe the IRS for the year, collected a little at a time so you don't face one large bill in April. The instructions for that guess come from Form W-4, which you fill out when you start a job and can update any time your situation changes.

The current W-4 no longer uses allowances. Instead it asks about your filing status, whether you hold more than one job, dependents you can claim, and any extra amount you want withheld. Each entry nudges your per-paycheck withholding up or down. Skipping the form doesn't skip the tax: your employer simply withholds at the default single rate, which is often more than a person with dependents actually owes.

• Step 1: filing status (single, married filing jointly, head of household)
• Step 2: multiple jobs or a working spouse, which raises withholding to match a higher combined bracket
• Step 3: dependent and other credits, which lower withholding
• Step 4: other income, deductions, and, in line 4(c), extra withholding you request per check

Federal income tax: brackets and the standard deduction

Federal income tax is progressive, meaning different slices of your income are taxed at rising rates rather than one flat rate on the whole amount. For the current tax year the brackets run 10%, 12%, 22%, 24%, 32%, 35%, and 37%, with the dollar thresholds depending on your filing status. A common misread is thinking that crossing into the 22% bracket taxes all your income at 22%; it doesn't. Only the dollars above that bracket's floor are taxed at 22%; everything below keeps its lower rates.

Before any of that applies, you subtract the standard deduction, income the government doesn't tax at all. For the current tax year it's about $16,100 for a single filer and roughly $32,200 for married couples filing jointly (illustrative figures; the IRS adjusts them annually). What remains after that subtraction is your taxable income, and that is the number the brackets act on.

Two rates are worth knowing. Your marginal rate is the bracket your last dollar falls in, useful for deciding what a raise or an extra shift is worth after tax. Your effective rate is total income tax divided by total income, which is always lower than the marginal rate because of the lower brackets and the deduction underneath. All bracket and deduction figures here are U.S. federal, current tax year, estimates only.

FICA: Social Security and Medicare

FICA is a separate, flat set of payroll taxes that fund Social Security and Medicare. Unlike income tax, it isn't affected by your W-4, your standard deduction, or your bracket; it comes off nearly every dollar of wages automatically, which is why your take-home is lower than an income-tax-only estimate would suggest.

Social Security is 6.2% of wages, but only up to an annual wage base (about $184,500 for the current year); earnings above that cap aren't subject to the 6.2%. Medicare is 1.45% with no cap. High earners pay an Additional Medicare Tax of 0.9% on wages above a threshold, $200,000 for single filers and $250,000 for married filing jointly. Your employer matches the base Social Security and Medicare amounts behind the scenes, though that match isn't part of your take-home math.

• Social Security: 6.2% of wages up to the annual wage base (about $184,500 this year)
• Medicare: 1.45% of all wages, no upper limit
• Additional Medicare: extra 0.9% on wages over $200,000 single / $250,000 joint
• None of these change with your W-4; they are fixed by law

A worked example: single filer earning $60,000

Take a single person with a $60,000 salary, the standard deduction, and no pretax deductions, for the current tax year. Start with taxable income: $60,000 minus the $16,100 standard deduction leaves $43,900.

Now apply the brackets to that $43,900. The first $12,400 is taxed at 10%, which is $1,240. The remaining $31,500 (from $12,400 up to $43,900) sits in the 12% bracket, which is $3,780. Add them together and the federal income tax is about $5,020. Notice the effective rate is only about 8.4% of the full $60,000, even though the top dollar is in the 12% bracket.

FICA is calculated on the full $60,000, not the taxable amount: Social Security is 6.2% of $60,000 = $3,720, and Medicare is 1.45% of $60,000 = $870, for $4,590 total. Subtract both taxes, $5,020 in income tax and $4,590 in FICA, and take-home is about $50,390 for the year, or roughly $1,938 on a biweekly (26-check) schedule. State income tax, where it applies, would come off on top of this. Every figure here is a current-tax-year estimate rounded for illustration, not an exact return.

• Taxable income: $60,000 minus $16,100 = $43,900
• Federal income tax: $1,240 (10%) + $3,780 (12%) = about $5,020
• FICA: $3,720 Social Security + $870 Medicare = $4,590
• Take-home: $60,000 minus $5,020 minus $4,590 = about $50,390/year (before state tax)

Why you get a refund or a bill, and how to fix it

A refund isn't a bonus; it means you had more withheld during the year than your actual tax turned out to be, and the IRS is returning the difference. Owing at tax time means the opposite: your paychecks came up short of the real bill. Neither is inherently good or bad, but a very large refund is an interest-free loan you made to the government, while a large balance due can sting and, if big enough, trigger an underpayment penalty.

The lever is your W-4. If you consistently get a big refund and would rather have that money in each paycheck, reduce withholding: claim the dependents and credits you're entitled to in Step 3, or make sure a since-departed second job isn't still inflating your rate. If you keep owing, increase withholding: the cleanest way is Step 4(c), where you enter a flat extra dollar amount to add to every check. Divide the shortfall by your number of remaining paychecks to size it.

Life events are the usual reason last year's W-4 stops fitting: marriage, a new baby, a second job, a raise, or a working spouse. Update the form when those happen rather than waiting for a filing-season surprise. Run your numbers through the calculator to see the projected refund or balance, then adjust one input at a time until withholding lands close to your actual tax.

What a pretax contribution really costs you

Pretax deductions lower the wages your income tax is computed on, so each dollar set aside costs less than a dollar of take-home. Use a single filer earning $95,000, with the same current-year standard deduction of $16,100 as the guide's example. With no deductions, taxable income is $78,900 and federal income tax is $1,240 + $4,560 + $6,270 = $12,070. FICA is 7.65 percent of $95,000, or $7,267.50, so take-home before state tax is $95,000 - $12,070 - $7,267.50 = $75,662.50.

Now put 6 percent, or $5,700, into a traditional 401(k). Taxable income falls to $73,200 and the tax to $10,816, a drop of $1,254, which is 22 percent of $5,700 because the contribution comes off the top of the 22 percent bracket. FICA is unchanged, because 401(k) deferrals still count as wages for Social Security and Medicare. Take-home is $95,000 - $5,700 - $10,816 - $7,267.50 = $71,216.50, down $4,446 rather than $5,700.

Health premiums paid through an employer cafeteria plan work slightly better, since they usually escape FICA as well as income tax. A $2,400 yearly premium saves 22 percent x $2,400 = $528 of income tax and 7.65 percent x $2,400 = $183.60 of FICA, a total of $711.60. A Roth 401(k) is different: it is taken from after-tax pay, so your income tax withholding does not change.

Bonuses and supplemental wages

Bonuses often look heavily taxed because employers may use a flat supplemental method rather than your regular schedule. Under the optional flat-rate method, federal income tax on supplemental wages is withheld at 22 percent for amounts up to $1 million in a year, with a higher mandatory rate on the excess. A $5,000 bonus has $1,100 of federal income tax withheld, $310 of Social Security, and $72.50 of Medicare. The total is $1,482.50 and the check arrives at $3,517.50 before any state tax.

The 22 percent is a prepayment, not the actual tax. Suppose the earner is single with $60,000 of salary. Adding the bonus makes income $65,000, taxable income $48,900, and the tax $5,620 against $5,020 before, an increase of only $600, because the entire bonus still sits in the 12 percent bracket. The $1,100 withheld exceeded the $600 owed by $500, which comes back as part of the refund at filing. Another method adds the bonus to the regular check and withholds as if the total were your usual pay, which can produce a different amount.

A bonus does not push all your pay into a higher bracket. Only the dollars above a bracket's floor are taxed at its rate, so a raise or bonus never lowers your take-home on the federal side.

Two jobs or two earners: why Step 2 of the W-4 exists

Each employer withholds as though its paycheck is your only income. That works for one job and fails for two, because both employers apply the full standard deduction and the low brackets. Take a married couple filing jointly where each spouse earns $60,000. On its own, each salary leaves taxable income of $60,000 - $32,200 = $27,800, and tax of $2,480 + $360 = $2,840, so the two employers withhold about $5,680 combined.

Their real return tells another story. Combined income of $120,000 less one $32,200 deduction is $87,800 of taxable income, and the tax is $10,040. The shortfall is $10,040 - $5,680 = $4,360, with no one at fault and nothing wrong with either paycheck. The deduction was counted twice.

Step 2 of the W-4 offers three routes: the IRS Tax Withholding Estimator, the multiple-jobs worksheet, or a checkbox for exactly two jobs with similar pay. Extra dollars on line 4(c) also work. The estimator is the most accurate and the checkbox the quickest. A $4,360 gap spread over 26 pay periods is about $168 per check, which shows the scale of the adjustment, and it is worth redoing after a raise or job change.

High earners and the Social Security cap

Social Security tax stops once your wages reach the annual base, so take-home rises partway through the year. Consider a single employee earning $250,000, paid biweekly, so $9,615.38 per check. Social Security is 6.2 percent of the first $184,500, or $11,439, and Medicare is 1.45 percent of everything, or $3,625. The Additional Medicare Tax adds 0.9 percent on wages above $200,000, which is $450. The total is $15,514, matching the Paycheck Tax Withholding Calculator.

The cap arrives in the 20th paycheck of the year. After 19 checks, wages are $182,692, so only $1,808 of the 20th check is subject to the 6.2 percent. From the 21st check on, Social Security drops out, and take-home rises by 6.2 percent of $9,615.38, about $596 per check. The extra Medicare tax begins on the check that carries year-to-date wages past $200,000, which is the 21st, and then takes about $86.54 per check.

Employers withhold the additional 0.9 percent above $200,000 regardless of filing status. The amount actually owed depends on your status when you file, with thresholds of $200,000 single and $250,000 joint, so a married couple can be over-withheld and recover the difference at filing.

Avoiding an underpayment penalty

The IRS expects tax to be paid through the year, not only in April. You can usually avoid the underpayment penalty if you owe less than $1,000 after withholding and credits, or if your withholding and payments cover at least 90 percent of this year's tax or 100 percent of last year's tax. The prior-year threshold rises to 110 percent for higher earners, with an adjusted gross income above $150,000.

Take the single filer from earlier, with a $12,070 tax bill, and suppose $11,000 was withheld across the year. The balance due is $1,070, which exceeds $1,000. The penalty still does not apply, because $11,000 / $12,070 = 91.1 percent, which is above the 90 percent test of $10,863. If withholding had been $10,500, that is 87 percent, and the penalty could apply unless the prior-year safe harbor was met.

Withholding gets credit as if it were paid evenly through the year, even when it came late, which is why a mid-year W-4 increase can fix a shortfall. Estimated tax payments get no such treatment and are judged by their dates. These are general rules, so confirm the details for your situation with the IRS instructions or a tax professional.

Pay frequency, the pay stub, and the W-2

The same salary yields different checks. On $60,000, a biweekly schedule pays 26 checks of $2,307.69, a semimonthly one pays 24 checks of $2,500, and federal income tax of $5,020 works out to $193.08 or $209.17 per check. Biweekly pay also creates two months a year with three paychecks. With $1,938 take-home per biweekly check from the guide's example, a normal month brings in $3,876 and a three-check month brings in $5,814, so budget from the average of $4,199 a month, not from one month.

Reconcile your stub against your W-2 at year end. Box 1 shows taxable wages for income tax, reduced by traditional 401(k) deferrals. Box 3 shows Social Security wages and Box 5 Medicare wages, both of which are normally higher than Box 1 when you contribute to a 401(k). Box 2 holds federal income tax withheld, Box 4 Social Security tax and Box 6 Medicare tax.

Compare the year-to-date column on your final stub of the year with those boxes, and ask payroll to explain any mismatch before you file.