Paper trip log or GPS app in Portugal: what AT accepts in 2026
Portugal's AT modernized mileage proof requirements. A side-by-side comparison of paper logs and GPS apps.
Where the Portuguese rule stands
Portugal's AT requires every reimbursable trip to be documented with origin, destination, business purpose, kilometers, and vehicle. The classic format is the *boletim itinerário* (paper trip log). AT Despacho 1138/2024 explicitly recognizes digital support when it meets three conditions: data integrity (no post-record alteration), auditability (timestamps + actor on every change), and reproducibility for inspection. Modern GPS apps satisfy all three.
Paper log weaknesses
Reconstructed from memory at week's or month's end, mileage estimated visually, folders lost, no timestamps to prove when entries were made. Inspections of teams >10 drivers, >1,500 km/month commonly find gaps.
GPS app strengths
Real route, deterministic km, immutable timestamps, digital signature chain (driver + approver), exportable PDF/CSV with integrity hash. AT has been low-friction with companies using this stack since the 2024 Despacho.
Where GPS fails
Forgot to start the trip (mitigate with auto-start by geofence), forgot to mark personal mode (mitigate with weekly approver review), drained battery (mitigate by accepting a digital manual form as complement). The hybrid stack — GPS for 90-95%, digital manual form for 5-10%, weekly approver — defends best.
Retention
Keep mileage records for the general 4-year tax prescription window; 6 years if there are open inspections.
Migration checklist
Choose an app that meets integrity + auditability + reproducibility, announce 30 days ahead, train approvers, run paper + GPS in parallel for 60 days, archive paper history as hashed PDFs, and update the internal policy and contract clause for location-data processing under Lei 58/2019 (Portugal's RGPD execution).