IMSS Work Risk Premium: How Accidents Become Payroll Cost in Mexico

A hand injury on a stamping line in November 2026 whose case closes in January 2027 is counted in the 2027 period, declared in February 2028 and paid on every payroll from March 2028 through February 2029. That lag is how the IMSS work risk premium works. The Mexican Social Security Institute (IMSS) insures registered employers against work injuries and occupational disease, and most employers price that coverage from their own record, one calendar year at a time.

How is the IMSS work risk premium calculated?

Article 72 of Mexico's Social Security Law (Ley del Seguro Social, or LSS) gives every employer the same formula: claims rate times a premium factor, plus a minimum.

Premium = [(S/365) + V × (I + D)] × (F/N) + M

LSS Art. 72, last amended DOF (Mexico's official gazette) January 15, 2026.

Cases count when they close between January 1 and December 31, whenever they happened (LSS Art. 74; RACERF Art. 32, section I, RACERF being the Social Security Law regulation on employer registration, classification and collection). Commuting accidents are excluded (LSS Art. 72). The percentage applies to contribution-base payroll, the salary figure behind all IMSS contributions, for the whole workforce.

Why one permanent disability outweighs years of sick days

Temporary disability days are divided by 365; permanent disabilities and deaths are multiplied by V, which is 28.

Take a 400-worker plant with 300 days of temporary disability in the year and no permanent cases. Those days add 0.82 inside the bracket, and the calculated premium is 0.97%. One permanent disability rated at 25% adds 7, the same weight as 2,555 days of temporary disability, and the calculation jumps to 5.00%. One death adds 28, equal to 10,220 days, and the result is 17.07% (calculated with LSS Art. 72).

Severity, far more than frequency, is what moves this premium.

N matters too: the same injury moves the premium of a 150-person plant far more than that of a 1,500-person plant.

New plants start at the class average premium

A company registering with IMSS for the first time, or changing activity, pays the average premium of the class assigned to its activity (LSS Art. 73):

LSS Art. 73.

From there, the annual review applies the formula (Art. 72); under RACERF Article 32, section IV, a new employer's first adjustment comes once it completes a full January to December period. A new entity in Mexico pays for its industry class until it has a full year of its own record.

For groups with several sites, RACERF Article 32, section VIII, sets a separate premium per municipality: a plant in the city of San Luis Potosí and another in Villa de Reyes file two premiums.

The February filing and the one-point cap

Article 74 of the LSS caps the change at one percentage point up or down from the previous year, and keeps every premium between 0.5% and 15% of contribution-base payroll. The 17.07% in the example is above that legal maximum, but the annual cap applies first:

Calculated with LSS Arts. 72 and 74.

The filing is due during February, unless the premium is unchanged (RACERF Art. 32, section V). The new rate runs from March 1 to the last day of the following February (section III), and IMSS can correct it, effective that same March 1 (section VI). If claims stay high, the premium climbs a point each year, and it comes down no faster. The cap softens a bad year, and it also means a high premium takes years to come back down.

Is San Luis Potosí a high-cost state for this premium?

IMSS, Statistical Report (Memoria Estadística) 2025, tables VII.1, VII.2, VII.3 and VII.35.

San Luis Potosí has slightly fewer workplace accidents per 100 workers than the national average and 58% more permanent disabilities, the fifth highest of 35 in the IMSS table. That is the variable the formula multiplies by 28. In San Luis Potosí, the premium story is about how badly people get hurt more than how often.

Commuting accidents run 34% above the national rate but stay out of the premium. Occupational diseases count once IMSS rates them: of the 683 recorded in the state in 2025, 480 (70%) were shoulder injuries, carpal tunnel and tenosynovitis, typical of assembly lines (IMSS, table VII.27). Our overview of workplace accidents in San Luis Potosí goes through the full data.

What lowers the premium over the next few years

Five levers act on that formula:

1. Put prevention where permanent injuries come from, following the Mexican standards for work at heights (NOM-009-STPS-2011), forklifts (NOM-006-STPS-2023), confined spaces (NOM-033-STPS-2015) and ergonomics (NOM-036-1-STPS-2018).
2. Focus on the first year in the job, when 48.2% of workplace accidents and occupational diseases nationwide happen (IMSS, Statistical Report 2025, table VII.12), with pre-employment exams through our occupational health services for plants and onboarding training with a DC-3, Mexico's official training record.
3. Keep a detailed record of each case from start to close (RACERF Art. 34) and review every rating notice IMSS sends (Art. 32, section V).
4. Document your prevention programs, which Article 74 of the LSS takes into account when the premium changes.
5. Get a safety management system accredited by STPS, which lowers F from 2.3 to 2.2 (LSS Art. 72), about 4% off the claims component.

A commuting accident recorded as a workplace accident raises the premium for no legal reason. Clean case records are the part of the premium you can fix at a desk.

Each point of premium equals 1% of a full year of contribution-base payroll: for every MXN 100 million of that payroll, one point is MXN 1 million. Serious accidents can also bring STPS fines in Mexico, which multiply per affected worker, and STPS compliance consulting for plants in San Luis Potosí works on both sides of that cost.