To calculate Box 1 on your W-2 from a pay stub, take your year-to-date gross pay, subtract your pre-tax deductions, and add any taxable fringe benefits. Use the final pay stub of the calendar year, usually dated in late December, and read only the YTD column. The number you land on is what will appear in Box 1 of the W-2 your employer sends by January 31.
The formula in one line:
YTD Gross Pay − Pre-Tax Deductions + Taxable Fringe Benefits = Box 1
Reading the Right Column on Your Pay Stub
Pay stubs typically show two sets of numbers side by side: the current pay period and year-to-date. Only the YTD figures matter here. Mixing up the columns is the single most common reason an estimate comes out wildly wrong.
Your YTD gross pay is the top-line number before anything comes out. It includes salary, hourly wages, overtime, bonuses, commissions, and reported tips. Bonuses and commissions belong in this total at their full pre-withholding amount, even when they arrived on a separate stub with heavy tax withheld. Withholding rates do not change what goes in Box 1.1Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
Scan the deductions section next. Most stubs group deductions as “Before Tax” and “After Tax,” or use codes. You want the YTD total of each pre-tax item. Post-tax deductions such as Roth 401(k) contributions, union dues, and wage garnishments do not reduce Box 1 and should be left out of the math.
Finally, look for line items labeled as imputed income or taxable fringe benefits. Common labels include “GTL” for group-term life insurance and “Auto” for personal use of a company car. Their YTD amounts get added back after you subtract pre-tax deductions.
Pre-Tax Deductions That Reduce Box 1
Pre-tax deductions are why Box 1 is smaller than your gross pay. Your employer routes these amounts to qualified benefit plans before calculating federal income tax.
Traditional Retirement Contributions
Traditional elective deferrals to a 401(k), 403(b), or governmental 457(b) plan come off the top. For 2026, the standard limit is $24,500. Workers 50 and older can defer an additional $8,000, and workers aged 60 through 63 can defer an additional $11,250.2Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 These deferrals reduce Box 1 but stay subject to Social Security and Medicare taxes.3Internal Revenue Service. Government Retirement Plans Toolkit
Health Premiums and Cafeteria Plan Benefits
Premiums for medical, dental, and vision insurance paid through a Section 125 cafeteria plan are excluded from federal taxable wages.4Office of the Law Revision Counsel. 26 USC 125 – Cafeteria Plans Health care Flexible Spending Account contributions are pre-tax as well, capped at $3,400 for 2026.
Health Savings Account contributions made through payroll reduce Box 1. The 2026 annual limits are $4,400 for self-only coverage and $8,750 for family coverage.5Internal Revenue Service. Notice 2026-5 – Expanded Availability of Health Savings Accounts
Dependent Care and Commuter Benefits
Dependent care FSA contributions are excluded from Box 1 up to $7,500 per household for 2026, or $3,750 if married filing separately.6FSAFEDS. Dependent Care FSA Qualified transit passes and qualified parking benefits are each excludable up to $340 per month in 2026.7Internal Revenue Service. Publication 15-B (2026), Employer’s Tax Guide to Fringe Benefits
Roth Contributions Do Not Reduce Box 1
This is where estimates go wrong. Designated Roth 401(k) and Roth 403(b) contributions are after-tax. They appear on your pay stub next to your other retirement deductions, but they stay inside Box 1. On the W-2 they show up in Box 12 with code AA (Roth 401(k)) or BB (Roth 403(b)), which is informational only.8Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
If your stub combines traditional and Roth contributions under one “retirement” label, you’ll subtract too much and land on a Box 1 that’s too low. Check your plan enrollment or ask payroll to confirm the split before you subtract anything.
Taxable Fringe Benefits That Add to Box 1
Some employer-provided benefits count as income even though no cash reaches you. They increase Box 1.
Group-term life insurance over $50,000. Coverage above $50,000 generates imputed income based on an IRS age-based table, not on your employer’s actual premium.9Office of the Law Revision Counsel. 26 USC 79 – Group-Term Life Insurance Purchased for Employees A 45-year-old with $100,000 of employer coverage has imputed income of $90 for the year, calculated at $0.15 per $1,000 of excess coverage per month.7Internal Revenue Service. Publication 15-B (2026), Employer’s Tax Guide to Fringe Benefits
Personal use of a company vehicle. When you use an employer-provided vehicle for personal driving, the value of that use is taxable compensation and lands in Box 1.
Moving expense reimbursements. For most workers, employer-paid moving expenses are taxable. The Tax Cuts and Jobs Act suspended the moving expense exclusion starting in 2018, and the One, Big, Beautiful Bill Act made the change permanent. Only active-duty military and certain intelligence community members can still receive tax-free moving reimbursements.10Internal Revenue Service. Moving Expenses to and from the United States
Educational assistance over $5,250. Employer-paid tuition and education expenses are tax-free up to $5,250 per calendar year under Section 127. Anything above that gets added to Box 1.11Office of the Law Revision Counsel. 26 USC 127 – Educational Assistance Programs
A Sample Calculation
Here’s the math with realistic numbers. Suppose your final 2026 pay stub shows:
- YTD gross pay: $72,000
- Traditional 401(k) contributions: $6,000
- Health insurance premiums (Section 125): $3,600
- Health care FSA: $1,200
- HSA contributions: $2,400
- Roth 401(k) contributions: $2,000
- Group-term life imputed income: $54
Start at $72,000. Subtract the pre-tax items: $6,000 + $3,600 + $1,200 + $2,400 = $13,200. That leaves $58,800. The Roth contribution is not subtracted. Add the $54 in imputed life insurance income. Estimated Box 1: $58,854.
Why Your Estimate Won’t Match Box 3 or Box 5
Boxes 1, 3, and 5 rarely match, and that’s expected. Box 3 (Social Security wages) and Box 5 (Medicare wages) are calculated on a different set of exclusions. Traditional 401(k) and 403(b) deferrals reduce Box 1 but not Boxes 3 and 5, since those deferrals are still subject to payroll taxes.3Internal Revenue Service. Government Retirement Plans Toolkit Section 125 cafeteria plan deductions reduce all three boxes.
Box 3 also has a ceiling: the Social Security wage base of $184,500 for 2026.12Social Security Administration. 2026 Cost-of-Living Adjustment (COLA) Fact Sheet Medicare has no wage limit. High earners will see Box 3 capped, Box 5 running higher than Box 1, and Box 1 sitting somewhere in between depending on their pre-tax deductions.
When Your Estimate Doesn’t Match the Actual W-2
A gap of a few dollars is usually rounding across pay periods. A gap of hundreds or thousands means something was categorized differently than you assumed. The usual causes:
- Roth contributions treated as pre-tax by mistake.
- Imputed income for group-term life insurance that never appeared as a line item on your regular stubs.
- Mid-year benefit changes that make the YTD totals on your final stub incomplete.
- Third-party sick pay from an insurance carrier that lands in Box 1 without appearing on your pay stubs.
- Back pay or retroactive adjustments processed late in the year.
Payroll can pull a detailed wage register showing every dollar behind each W-2 box. Start there. If the register confirms a genuine error rather than a categorization you missed, ask for a corrected Form W-2c.13Internal Revenue Service. W-2 – Additional, Incorrect, Lost, Non-Receipt, Omitted