What moves Box 1 on your W-2

The subtractions are the familiar ones: the 401(k), the health premiums, the flexible spending account, the HSA. The additions are the ones that surprise people in January: the life insurance over $50,000, the personal miles on the company car, the health insurance an S corporation pays for its owner, the bonus that was “grossed up.” Boxes 3 and 5, the Social Security and Medicare wages, follow different rules, which is why the three numbers rarely match. This article is the list, in both directions, with the 2026 limits.

Three boxes, three answers

Box 1 is federal income tax wages: gross pay, less the deductions that are excluded from income tax, plus the taxable benefits. It is the number that goes on line 1a of the 1040. Box 3 is Social Security wages: the same gross pay, less only the deductions that are excluded from Social Security tax, capped at the wage base ($184,500 for 2026). Box 5 is Medicare wages: the same as Box 3 with no cap. Box 16 is Colorado wages, which equals Box 1 for almost everyone.

The reason they differ is one rule: retirement deferrals come out of Box 1 but not Boxes 3 and 5; cafeteria-plan deductions (health premiums, FSA, HSA through payroll, commuter benefits) come out of all three. Taxable benefits go into all three, with one common exception: health insurance paid for a 2%-or-more S corporation shareholder goes into Box 1 but not Boxes 3 and 5.

What comes out

Every dollar in this list is a dollar you earned and did not pay income tax on. The cafeteria-plan items also escape Social Security and Medicare tax (FICA), which at 7.65% is often the bigger saving for a middle-income household. The 2026 limits:

• 401(k), 403(b) and 457(b) elective deferrals: $24,500 (up from $23,500). Catch-up at age 50 and over, $8,000; at ages 60 to 63, $11,250. Saves income tax, not FICA.
• SIMPLE IRA deferral: $17,000, with a $4,000 catch-up ($5,250 at ages 60 to 63). Income tax only.
• Health, dental and vision premiums, the employee share, through a Section 125 plan: no limit. Saves income tax and FICA.
• Health FSA: $3,400 (up from $3,300). Income tax and FICA.
• HSA: $4,400 self-only, $8,750 family, plus $1,000 at age 55. Saves FICA only when the contribution runs through payroll.
• Dependent care FSA: $7,500, up from $5,000 ($3,750 married filing separately). Income tax and FICA.
• Transit pass and parking: $340 a month each. Income tax and FICA.
• Educational assistance, including student loan payments: $5,250. Income tax and FICA.

Three things people get wrong. The HSA saves FICA only if the contribution runs through payroll; a deposit you make yourself is deducted on Schedule 1 and gets the income tax back but not the 7.65%. The dependent care FSA jumped to $7,500 for 2026 under the 2025 tax law, and anything over the limit shows up in Box 10 and gets added back on Form 2441. And a Roth 401(k) contribution reduces nothing on the W-2; it is after-tax by design and is reported in Box 12 (code AA).

What the exclusion is worth: a $5,000 health FSA election for someone in the 22% bracket saves $1,100 of federal tax, $220 of Colorado tax and $383 of FICA, $1,703 in all, or 34% of the money. The same $5,000 put in a 401(k) saves $1,320, because the FICA is still paid. Both beat the same dollars taken home and spent.

What goes in

Anything of value an employer provides is wages unless a specific section of the Code excludes it. The common additions:

• Group-term life insurance over $50,000: the IRS cost of the coverage above $50,000, less anything the employee paid after tax. Box 12 code C. A $200,000 policy on a 52-year-old adds $414 a year. More below.
• Personal use of a company vehicle: commuting and personal miles valued by the cents-per-mile rule (72.5 cents for 2026, for vehicles worth up to $61,700 when first provided), the annual lease value table, or $1.50 per one-way commute. The employer may skip income tax withholding on it, but Social Security and Medicare are always withheld.
• S corporation health insurance for a 2%-or-more shareholder: the premiums the corporation paid are in Box 1 and Box 16, not in Boxes 3 and 5, labeled in Box 14. The shareholder then deducts them on Schedule 1 as self-employed health insurance. If the premiums are not on the W-2, the deduction is lost.
• Bonuses, awards and prizes: cash and gift cards of any amount; achievement awards above $1,600 ($400 for a non-qualified plan). Length-of-service and safety awards of tangible property within those limits are excluded; a Visa card never is.
• Gross-ups: the extra wages an employer adds so a benefit arrives net of tax. The gross-up is itself wages.
• Moving expenses: all employer-paid or reimbursed moving costs are taxable wages (2018 through at least 2028 under the 2025 law, except for active-duty military on orders).
• Nonqualified deferred compensation: in Boxes 3 and 5 when it vests, in Box 1 when paid.
• Stock: the spread on a nonstatutory option exercise (code V), restricted stock and RSUs when they vest, the discount on an ESPP disqualifying disposition. All wages, and the brokerage 1099-B will show a basis that does not include it unless corrected.

Excluded, and therefore not in any box: health coverage itself (code DD is information only), de minimis items (the holiday ham, the office coffee), working-condition fringes (the laptop, the professional dues), employee discounts, accountable-plan reimbursements, employer retirement contributions and matches, up to $5,250 of educational assistance, and a cell phone used mainly for business.

Group life over $50,000

Employer-paid group-term life insurance is tax-free up to $50,000 of coverage. Above that, the IRS’s cost of the excess coverage, not the employer’s actual premium, is wages, computed monthly from the age table and reduced by anything the employee paid toward the policy with after-tax dollars. It is in Boxes 1, 3 and 5 and shown in Box 12 with code C. The table runs from 5 cents per $1,000 of coverage per month under age 25 to 23 cents at ages 50 to 54, 66 cents at 60 to 64 and $2.06 at 70 and over, using your age on December 31. The 52-year-old above: 150 times 23 cents times 12 months is $414.

For a retiree whose former employer keeps the coverage, the same amount shows up on a W-2 with no cash to withhold from, which is how a retired teacher ends up owing Social Security tax. Coverage on a spouse or dependent over $2,000 is also taxable and gets no $50,000 exclusion.

The gross-up

An employer that gives an employee a $500 holiday bonus and wants the employee to net $500 has a problem: the $500 is wages, so withholding comes out of it. The fix is to pay more than $500, enough that after withholding on the whole amount, $500 is left. But the extra is also wages and also taxed, and so on. The series converges, and the formula is simple: gross equals net divided by (1 minus the combined withholding rate). The same arithmetic applies to any benefit delivered net of tax: a taxable moving reimbursement, a prize, an executive’s club dues.

The IRS worksheet example: a $500 net bonus with 7.65% FICA, 15% federal and 5% state withholding. One minus 0.2765 is 0.7235; $500 divided by 0.7235 is $691.09 gross, of which $52.87 is FICA, $103.67 federal, $34.55 state, and $500.00 reaches the employee. The $691.09 is in Boxes 1, 3 and 5. The gross-up only guarantees the net on payday; the actual tax in April may be more or less. An employer can also skip the gross-up and withhold from the next regular paycheck; the benefit is taxable either way.

Box 12 and Box 14, decoded

Box 12 carries lettered codes. Code C is taxable group life, already in Box 1, nothing to do. Codes D, E, G and S are 401(k), 403(b), 457(b) and SIMPLE deferrals, already out of Box 1; they may support the Saver’s Credit. AA and BB are Roth 401(k) and 403(b), no deduction, counted toward the same limit. DD is the total cost of employer health coverage, information only. W is HSA contributions, employer and payroll, which go on Form 8889 and reduce what you may still contribute yourself. V is income from exercising nonstatutory stock options, already in Box 1; add it to the basis of the shares sold. T is adoption benefits, and II is Medicaid waiver payments that can count as earned income for the EITC.

Box 14 is the employer’s free-text box, and what lands there depends on the payroll company: S corporation health insurance (needed for the Schedule 1 deduction), union dues, Colorado FAMLI premiums (not deductible), PERA contributions, personal use of the vehicle, charitable payroll deductions. Box 14 items are not in Box 1 unless the item is taxable; read the label. Box 10 is dependent care benefits and feeds Form 2441; Box 13 tells the IRS you were covered by a retirement plan, which decides whether your IRA contribution is deductible.