Every month there are two calculations of the same contributions. One is made by the IMSS (Mexican Social Security Institute) using the enrollment movements you filed: that is the emisión (billing). The other you make yourself in SUA, the IMSS desktop system for calculating and paying contributions, using your payroll. Reconciling means putting both side by side to find differences before you pay.
Why does it matter? If you pay with a SUA file that does not match the billing, you will most likely receive assessments later, or you may have overpaid. Checking in time lets you correct things calmly.
What you need
- The IMSS billing. Download it from the IMSS portal under IMSS desde su empresa → Emisión → Descarga de emisión. There is a monthly one (EMA) and a bimonthly one (EBA), in formats such as Excel or Visor.
- Your .SUA file for the same period, which is the payment file SUA generates.
- If you want to review mortgage credits: the enrollment movements and the Infonavit (workers' housing fund) withholding notices in CSV, downloaded from the Infonavit Employer Portal.
Before starting, confirm both files belong to the same employer registration number and the same period. It sounds obvious, but it is the most repeated mistake.
Two levels of review
First you see whether there is a difference; then where it is.
- Totals by item. In the EMA: fixed fee, excess, cash benefits, pensioners' medical expenses, work risk, disability and life, and childcare. In the EBA: retirement, old-age and severance, and Infonavit contributions and loan repayments.
- Employee-level detail. Headcount, contribution base salary (SBC), days contributed, hires, rehires, terminations, salary changes, disability leaves, absences, Infonavit credits and names.
Step by step
- Download the billing for the period you are about to pay.
- Generate the .SUA file with that period's payroll.
- Compare totals item by item. If they all match, you are most likely ready to pay.
- If any total differs, go to the detail and find the employees with different salaries, days or movements.
- Fix in SUA whatever is missing or extra (hires, terminations, salary changes, disability leaves…), generate the .SUA again and compare once more until it matches.
With large headcounts, doing this by hand in a spreadsheet takes hours. A reconciliation tool does it in seconds.
How to read each difference
- An employee appears in the billing but not in your SUA, or vice versa: a hire or termination was not entered.
- The SBC is different: check whether the salary change was filed with the IMSS, or whether it still needs to be entered in SUA.
- Days do not match: review disability leaves and absences for the period.
- The Infonavit credit does not match (EBA): review withholding, suspension or discount-change notices.
How often?
Once a month before paying the EMA, and every two months before paying the EBA. Contributions are due no later than day 17 of the following month, so ideally you compare as soon as the billing is available and your SUA is ready; that gives you room to correct.
In Nomikhor, the billing (EMA and EBA) is downloaded directly and compared in a Nomikhor–SUA–IDSE reconciliation; thanks to the IDSE connection (the IMSS online filing system) and the SUA export, movements come from the same payroll you calculated.