Final answer:
For tax-free per diem eligibility, travel assignments must not exceed a certain length, typically around 12 months or less.
Step-by-step explanation:
Tax-free per diem eligibility is a term used in business to refer to the reimbursement of daily expenses for work-related travel. In order to be eligible for tax-free per diem, a travel assignment must not exceed a certain length, which is usually determined by the employer or agreed upon by industry standards. While the specific length may vary, it is typically around 12 months or less.