Page "Per diem" Paragraph 4

To qualify for per diem, work-related business activity generally requires an overnight stay.

The IRS code does not specify a number of miles.

However, based on case precedent and IRS rulings, it is commonly accepted that an overnight stay is required and actually occurs to justify payment of per diem allowance.

The purpose of the per diem payment ( or the deduction of expenses when inadequate reimbursements are provided ) is to alleviate the burden on taxpayers whose business or employment travel creates duplicated expenses.