Originally Posted by
der_saeufer
The assumptions used by the two agencies are different--to oversimplify it a bit, GSA assumes you're a civil servant going to meetings in an office with other civil servants so you just need some decent food. State assumes you're a diplomat potentially going to fancy dinners with your foreign counterparts and may need to spend a bit to pay your part of the bill. This leads to State's M&IE being significantly higher than GSA's even when the cost of restaurants in the foreign city is lower than that in a major US city. (See, e.g. M&IE rates for Mexico City or Berlin vs. NYC)
Incidentals is sort of a catch-all for stuff like toothpaste and razor blades domestically, and it's always $5/day. Overseas it also includes things like laundry and is higher.
This is the answer to the question. As to the methodology:
The M&IE portion is intended to substantially cover the cost of meals and incidental travel expenses such as laundry and dry cleaning. The maximum per diem rates for foreign countries are based on costs reported in the Hotel and Restaurant Survey (Form DS-2026) submitted by U.S. government posts in foreign areas. This report includes prices for hotel rooms and meals at facilities representative of moderately priced and suitable hotels and restaurants most frequently used by typical Federal travelers.
(Form DS-2026 if really interested
https://aoprals.state.gov/Content/documents/DS-2026.pdf)
Further, the Department of State publishes a breakdown of suggested split by meal, plus incidentals, for all per diem levels, at
https://aoprals.state.gov/content.as...114&menu_id=75 .