Per diem pay puts more money in a driver’s pocket by lowering taxable income. The IRS has no problem with that. But the pay structure helping at tax time can cause a health plan to fail the ACA affordability test, because per diem reimbursements don’t show up in the wage number the W-2 Safe Harbor relies on.
The W-2 Wage Safe Harbor checks affordability against Box 1 wages, not total driver compensation. Carriers that set contributions based on gross pay, rather than Box 1, can pick the wrong safe harbor and fail without knowing it.
How Does Per Diem Pay Reduce Box 1 Wages?
Per diem lets drivers receive tax-free reimbursement for meals and incidental expenses while away from home, up to the IRS’s special transportation industry rate of $80 per day within the continental United States (Rev. Proc. 2019-48, as extended by IRS Notice 2025-54 through Sept. 30, 2026). It is a standard, legitimate pay structure across trucking.
Per diem amounts are excluded from Box 1 of the W-2, which reports only taxable wages. A driver earning $65,000 in total compensation with $15,000 paid as per diem has a Box 1 wage of just $50,000.
That creates a gap. Carriers that size health plan contributions against total compensation are testing affordability against a number the IRS never uses.
Where Does the Calculation Break Down?
The W-2 Safe Harbor tests the employee’s contribution against 9.96% of Box 1 wages for 2026. A lower Box 1 figure means a lower affordability ceiling. If contributions are set against gross pay instead, the plan can fail the W-2 Safe Harbor without anyone catching it.
Timing makes this worse. Box 1 wages aren’t final until year-end, so the W-2 Safe Harbor cannot be confirmed until the plan year is already over. For carriers with a large per diem population, that turns affordability into a retroactive risk.
How Does Rate of Pay Compare With Per Diem Pay?
Rate of Pay is generally the better fit here. It multiplies the hourly rate by 130 hours per month, so per diem allocation has no effect on the result, and it can be calculated prospectively instead of waiting on year-end wage data.
The other two safe harbors work, but each comes with a tradeoff when per diem is in play.
Why Is the Federal Poverty Line Safe Harbor a Fallback, Not a First Choice?
It sets a fixed monthly contribution cap, currently $129.89 for the mainland United States in 2026, and per diem has no effect on it either. But the cap is often lower than what a Rate of Pay calculation allows, so it can force a greater contribution than necessary for higher-paid drivers.
Why Is the W-2 Safe Harbor Risky for Drivers?
It suits salaried employees with stable income and no significant non-taxable pay. For a per diem-heavy driver population, it carries real risk, because per diem dollars are excluded from Box 1, so the wage base it tests against gets smaller.
The IRS allows different safe harbors for different employee classes, as long as the choice is documented and applied consistently. A carrier can use Rate of Pay for hourly drivers and W-2 for salaried dispatchers in the same plan year.
Check which safe harbor each employee class is coded under on Line 16 of Form 1095-C. If W-2 is applied broadly across a driver population with high per diem, rerun the calculation using Rate of Pay (hourly rate x 130 hours) instead.
How Should Carriers Match Safe Harbors to Driver Pay?
Per diem pay never breaks affordability on its own. Pairing it with the wrong safe harbor does. Rate of Pay tests what drivers actually earn each hour, not the taxable slice left after per diem, so it holds up regardless of how a paycheck is structured.
Trusaic’s ACA Compliance solution validates safe harbor selection against actual Box 1 data before forms reach the IRS AIR System. Talk to Trusaic to confirm each driver class is coded correctly before your next filing.
