Reimbursing employees from a Mexican RESICO company: step by step
How to reimburse employees for mileage without it being reclassified as salary under IMSS and ISR.
The central risk
SAT and IMSS share one doctrine: any periodic fixed payment to a worker is presumed salary. A flat MXN 4,000/month for 'fuel' with no variation and no logbook gets reclassified as salary, triggering ISR + IMSS contributions, surcharges, and penalties. To avoid that, mileage reimbursement must vary with real travel and be backed by a trip log.
Step 1: written policy
The policy belongs in the Internal Work Regulation (RIT) or as an annex to the individual contract. It must specify eligibility, the per-km rate and how it's updated, eligible vs ineligible trips, the submission deadline (recommend: by end of the following month), and required documentation (logbook + fuel CFDIs).
Step 2: mandatory logbook
Each trip must record date, origin, destination, specific business purpose, kilometers, and client/project. SAT accepts paper, spreadsheet, or app — what matters is that it exists and is consistent. GPS apps are the most defensible because the number doesn't depend on the employee's memory.
Step 3: defensible per-km rate
SAT publishes no official rate. The Mexican market in 2026 runs MXN 5-8/km depending on vehicle and region. Document the methodology (fuel + maintenance + depreciation), review quarterly against published fuel prices, and apply the same rate to comparable roles.
Step 4: payment route
Pay through payroll under a separate code labeled 'Reimbursement – mileage' (never 'bonus' or 'compensation'), or via a separate transfer referencing the period's logbook. Both are valid; payroll is simpler for reconciliation, separate transfers are more visibly non-salary.
Step 5: CFDI and accounting
The reimbursement is deductible under ISR Law Art. 25 as a necessary expense. Fuel CFDIs paid by the employee must be issued in their name and attached to the logbook. Book the reimbursement to 'travel expenses' or 'selling expenses', not 'wages'.
Step 6: quarterly IMSS exposure review
Each quarter, compute reimbursement / nominal salary by employee. If the ratio exceeds 30% for anyone, run a specific review: is variability real (40-160% of the period average)? Does the logbook back every peso? Are there zero-km periods (vacation, leave)? IMSS reclassification visits target employees with effectively identical payments for 12 months.
Errors that trigger penalties
1. Identical fixed monthly payment for more than 6 months. 2. Year-end logbook reconstructed from memory. 3. Missing or third-party-issued fuel CFDIs. 4. Reimbursement >50% of base salary with no documentary justification. 5. Policy not signed or unchanged for 3 years.