Before you calculate any IMSS (Mexican Social Security Institute) contribution, you need to know exactly which payroll items make up the contribution base salary (SBC, salario base de cotización). The general rule is broad: everything given to the employee for their work is included, whether cash paid by daily rate, bonuses, earnings, meals, housing, premiums, commissions, benefits in kind or any other amount. The exceptions are in article 27 of the Social Security Law (LSS), which lists what is left out.
Quick reference table
| Item | Included? | Legal basis |
|---|---|---|
| Salary, aguinaldo (year-end bonus) and vacation premium | Yes, through the integration factor | Art. 27, first paragraph |
| Sunday premium, commissions and rest days worked | Yes, in full | Art. 27, first paragraph |
| Work tools | No | Cl. I |
| Savings fund meeting the requirements | No | Cl. II |
| Employer contributions to retirement and housing | No | Cl. III and IV |
| PTU (mandatory profit sharing) | No | Cl. IV |
| Meals and housing at a cost to the employee | No, if the employee pays at least 20 % | Cl. V |
| Grocery vouchers | Only the amount above 40 % of the UMA | Cl. VI |
| Punctuality and attendance bonuses | Only the amount above 10 % of the SBC, each one separately | Cl. VII |
| Pension plans | No, if they meet the requirements | Cl. VIII |
| Overtime | No, as long as it stays within Federal Labor Law (LFT) limits | Cl. IX |
The UMA (Unidad de Medida y Actualización) is the official reference unit that replaced the minimum wage as an index in laws.
Watch out for
- Accounting records: no item can be excluded unless it is properly recorded in the company's books.
- Minimum wage reads as UMA: clauses V and VI mention the minimum wage, but since the 2016 de-indexation those references are applied in UMA.
- Excess amounts: grocery vouchers and punctuality and attendance bonuses are not fully excluded; whatever exceeds the limit is added to the SBC.
Legal basis
- Social Security Law, article 27 (latest amendment published in the DOF on January 15, 2026).
- Federal Labor Law, articles 66 and 67 (overtime limits).
If your employees have earnings that change every period, continue with how to calculate the bimonthly variable salary update.
In Nomikhor, the integration factor updates on each employee's work anniversary and the bimonthly variable salary is calculated automatically, so the SBC you send through the IDSE connection (the IMSS online filing system) comes out right.