The EMA (IMSS monthly billing statement) has one line that changes from company to company: occupational risk insurance. Its percentage is called the occupational risk premium (prima de riesgo de trabajo) and it is reviewed every year based on your company's accident record. Fewer workplace accidents and occupational illnesses can lower it; more can raise it.
The formula and what each letter means
Article 72 of the Social Security Law (LSS) defines it as follows:
Premium = [(S / 365) + V × (I + D)] × (F / N) + M
| Letter | Meaning |
|---|---|
| S | Total days of temporary disability benefits from occupational risks closed during the year. |
| I | Sum of the permanent disability percentages (partial and total), divided by 100. |
| D | Deaths from occupational risks. |
| N | Average number of employees exposed to risk: days contributed in the year divided by 365. |
| V | 28, the average length of working life in years. |
| F | 2.3, the premium factor. |
| M | 0.005, the minimum premium (0.5 %). |
The formula gives you a fraction; multiply it by 100 to read it as a percentage.
Worked example
Picture a company with 40 employees all year (40 × 365 = 14,600 days contributed), 60 days of disability benefits and no permanent disabilities or deaths:
- N = 14,600 / 365 = 40
- S / 365 = 60 / 365 = 0.16438
- V × (I + D) = 28 × (0 + 0) = 0
- Premium = 0.16438 × (2.3 / 40) + 0.005 = 0.00945 + 0.005 = 0.01445, that is, ≈ 1.4452 %
Limits that apply
- From one year to the next, the premium cannot go up or down by more than one percentage point (1 %).
- It always stays between a minimum of 0.5 % and a maximum of 15 %.
For example: if last year you had 2.5 % and the formula gives 0.8 %, your new premium will be 1.5 %, because it can only drop one point.
What is and is not counted
- Only occupational risks closed during the calculation period count, which runs from January 1 to December 31 of the previous year.
- Accidents while commuting (from home to work or back) are not counted.
Filing calendar
The annual filing is made in February, no later than the last business day of the month, with the previous year's data. The new premium applies from March 1 to the last day of February of the following year, so in March you need to update it in your SUA (the IMSS payment software) before calculating contributions.
Preparation checklist
- In January, gather the year's closed risks with their disability days and disability percentages.
- Confirm the year's days contributed, since N comes from them.
- Check that occupational-risk sick leave is correctly entered in your SUA; comparing it against the IMSS statement helps you spot errors.
Legal basis
- Social Security Law, article 72 (premium formula).
This article is for information only; check your specific case against current IMSS rules or with your advisor.
Once you have your new premium, Nomikhor calculates IMSS contributions automatically, and the Nomikhor–SUA–IDSE reconciliation helps you catch differences, such as sick leave entered incorrectly, before you pay.