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.