IMSS Contributions in Mexico: What the Worker Pays and What the Employer Pays

A Mexican payslip shows a single line for the worker's IMSS deduction, and that single line hides how the social-security bill is actually built. Every contribution to the Instituto Mexicano del Seguro Social (IMSS, the public social-security institute) is split across insurance branches (seguros), and most branches charge the employer and the worker at different rates on the same base. For a mid-salary worker the employee pays roughly 2.6 percent of that base, and the employer pays close to seven times as much. Anyone running Mexican payroll for clients has to compute both sides, branch by branch, and the branches do not share a single percentage.

The base every branch is computed on: the SBC and its two limits

Almost every IMSS contribution is a percentage of the Salario Base de Cotización (SBC, the integrated daily contribution wage): base pay plus the daily-equivalent value of statutory benefits such as the aguinaldo and the vacation premium. The SBC is a daily figure, and two boundaries on it govern the whole calculation.

The first is the ceiling. The SBC is capped at 25 times the UMA (Unidad de Medida y Actualización, the reference unit that replaced the minimum wage for indexing contributions). For 2026 the UMA is MXN$117.31 a day (INEGI, effective 1 February 2026), so the SBC ceiling is 25 × 117.31 = MXN$2,932.75 a day. A worker earning above that contributes as if the SBC stopped at the ceiling; the contributions do not increase past that point.

The second is a threshold at 3 UMA (3 × 117.31 = MXN$351.93 a day in 2026). One health component applies only to the part of the SBC above that line, which means two workers in the same company can face different branch counts depending on whether their SBC clears 3 UMA.

Enfermedad y Maternidad: one branch, four components, two payers

The health and maternity branch (Enfermedad y Maternidad) is where most of the branch-by-branch detail lives, because it has four separate components and each treats the two payers differently (Ley del Seguro Social, Arts. 25, 106, 107).

• Cuota fija: the employer pays 20.40 percent of one UMA per worker, a flat per-head charge of about MXN$727 a month in 2026 regardless of salary (Art. 106, frac. I). The worker pays nothing toward it. Because the charge is fixed per head rather than a percentage of pay, it is a larger share of a low-wage worker's pay than of a high earner's. The 20.40 percent is the fully phased-in figure, not the rate written in the statute: LSS Art. 106, frac. I sets a base of 13.9 percent, which the law's Décimo Noveno Transitorio raised by 0.65 point each year from 1998 through 2007 to reach the 20.40 percent in force today.
• Cuota adicional (the excedente): on the part of the SBC above 3 UMA only, the employer pays 1.10 percent and the worker pays 0.40 percent (Art. 106, frac. II). Below 3 UMA neither side pays this component.
• Prestaciones en dinero (cash benefits): employer 0.70 percent, worker 0.25 percent of the full SBC (Art. 107).
• Gastos médicos para pensionados (retirees' medical costs): employer 1.05 percent, worker 0.375 percent of the SBC (Art. 25).

Invalidez y Vida, and the two retirement branches

Three more branches follow the same split-rate pattern, with the employer share several times the worker share.

Invalidez y Vida (disability and life) is 1.75 percent for the employer and 0.625 percent for the worker, both on the SBC (Ley del Seguro Social, Art. 147).

Retiro (the retirement sub-account) is 2.00 percent, paid entirely by the employer (Art. 168, frac. I). The worker contributes nothing to this branch, and it should never appear as a deduction on the payslip.

Cesantía en Edad Avanzada y Vejez (CEAV, severance in old age and old-age pension) is the branch that changes every year. The worker rate is fixed at 1.125 percent of the SBC (Art. 168, frac. II). The employer rate is progressive and rising: under the 2020 pension reform (Reforma de Pensiones, DOF 16 December 2020) the employer contribution increases in annual steps from 2023 through 2030. For 2026 the employer CEAV rate runs from 3.150 percent at one minimum wage up to 7.513 percent for a worker whose SBC exceeds 4.01 UMA (the top rate keeps rising each year to 11.875 percent in 2030, where the schedule ends). For a well-paid worker, CEAV is the single largest line on the employer's IMSS bill, and next year's rate will be higher again.

Riesgos de Trabajo, Guarderías, and INFONAVIT: the employer-only lines

Three further contributions fall entirely on the employer and never touch the worker's deduction.

Riesgos de Trabajo (occupational-risk insurance) funds benefits for work injuries and is the one rate an employer partly controls. Each employer is assigned a risk class by activity, with a base premium from about 0.54 percent for office work (Class I) up to about 7.59 percent for mining and hazardous work (Class V) (Ley del Seguro Social, Arts. 71-74). Each employer then recalculates its own premium annually from its accident record and files the result with IMSS by the end of February, so the number used this year is often not the number used last year. The premium can never fall below 0.50 percent or exceed 15.00 percent.

Guarderías y Prestaciones Sociales (daycare and social benefits) is a flat 1.00 percent of the SBC, employer-only (Art. 211).

INFONAVIT is administered separately from IMSS. The housing fund (Instituto del Fondo Nacional de la Vivienda para los Trabajadores) takes 5.00 percent of the SBC into each worker's housing sub-account (Ley del INFONAVIT, Art. 29). It uses the same SBC and the same 25 UMA ceiling, it is collected on the same bimonthly cycle as the retirement branches, and it is an employer cost, not a worker deduction. INFONAVIT is a housing contribution, not an IMSS branch, but any full picture of the payroll-borne social bill includes it.

One worker, both sides of the bill

Take a worker with an SBC of MXN$1,000 a day, about MXN$30,400 a month, at a Class I office employer. The SBC clears 3 UMA and stays below the 25 UMA ceiling, so every branch applies at its normal rate. Monthly 3 UMA is MXN$10,698.67, so the excedente base is 30,400 − 10,698.67 = MXN$19,701.33.

The worker's five deductions:

• Excedente, 0.40% of 19,701.33 = MXN$78.81
• Prestaciones en dinero, 0.25% of 30,400 = MXN$76.00
• Gastos médicos pensionados, 0.375% of 30,400 = MXN$114.00
• Invalidez y Vida, 0.625% of 30,400 = MXN$190.00
• CEAV, 1.125% of 30,400 = MXN$342.00

Total worker IMSS deduction: MXN$800.81 a month, about 2.6 percent of the SBC.

The employer's nine IMSS lines on the same worker:

• Cuota fija: MXN$727.51
• Excedente, 1.10%: MXN$216.71
• Prestaciones en dinero, 0.70%: MXN$212.80
• Gastos médicos pensionados, 1.05%: MXN$319.20
• Invalidez y Vida, 1.75%: MXN$532.00
• Riesgos de Trabajo, Class I 0.54355%: MXN$165.24
• Guarderías, 1.00%: MXN$304.00
• Retiro, 2.00%: MXN$608.00
• CEAV, 7.513% (SBC above 4.01 UMA): MXN$2,283.95

Total employer IMSS: about MXN$5,369 a month, roughly 17.7 percent of the SBC, close to seven times the worker's deduction. Add the 5.00 percent INFONAVIT housing contribution (MXN$1,520) and the employer's payroll-borne social cost reaches about MXN$6,889, near 22.7 percent of the SBC. The worker sees MXN$801 come off the payslip; the employer pays the rest on top of wages.

The four moving parts: the 3 UMA threshold, the risk class, the annual CEAV step, and the UMA ceiling

Four features make this calculation harder than looking up a single rate, and each is a place a static spreadsheet quietly falls out of date.

The 3 UMA threshold on the excedente means the branch count depends on the worker's SBC. The threshold has to be recalculated in pesos every time the UMA changes; otherwise a low-SBC worker is charged for a component that does not apply to them.

The Riesgos de Trabajo premium varies by risk class and is re-filed annually from each employer's own accident record, so two clients in different industries pay different rates, and the same client's rate changes from one year to the next.

The CEAV employer rate rises every year through 2030 under the pension reform, and it is progressive across eight SBC brackets, so a raise can shift a worker into a higher employer rate bracket mid-schedule.

The 25 UMA ceiling and the UMA itself reset each February, which rescales the cap, the cuota fija, and the 3 UMA threshold in one move.

Flux keeps each of these current: the UMA-driven ceiling and thresholds, the annual CEAV step, the per-employer risk premium, and both the employer and worker rate for every branch, so each pay period computes on this year's numbers rather than last year's. In Mexico the worker's IMSS deduction is the small, visible part of the contribution. The larger part is the employer's, spread across nine lines that each change on their own schedule.