Short answer: The W-2 safe harbor lets an ALE measure ACA affordability against the employee’s Box 1 W-2 wages: coverage is affordable if the required self-only contribution doesn’t exceed the annual affordability percentage (9.96% for 2026) of those wages.
The W-2 safe harbor is one of three IRS-approved methods applicable large employers (ALEs) can use to determine whether their health coverage is “affordable” under the ACA’s employer mandate.
Under this method, the employer looks at the employee’s Box 1 wages and ensures the required contribution for self-only coverage does not exceed the affordability percentage (9.96% for 2026) of those wages.
Example: if an employee’s Box 1 wages for the year are $40,000, the maximum affordable premium they can be required to pay is $40,000 × 9.96% = $3,984 per year, or about $332 per month.
This method requires the employer to use W-2 income from that same calendar year, which means affordability can only be confirmed after year-end once wages are final. Because it is based on actual income, it is less predictable than the other safe harbors but useful for variable-income employees.