ICSOE and SISUB: 2026 filing calendar and deadlines

A company that provides specialized services files two informational returns every four months: the ICSOE with the Mexican Social Security Institute (IMSS) and the SISUB with the workers' housing fund (Infonavit). The law gives both the same day: no later than January 17, May 17 and September 17, for the four months just ended. When that day falls on a weekend or a non-working day, the IMSS extends the ICSOE deadline to the next working day; for the SISUB there is no written rule.

The calendar

The three date columns say different things:

• The day set by law. «Cuatrimestralmente a más tardar el día 17 de los meses de enero, mayo y septiembre» (every four months, no later than the 17th of January, May and September; Social Security Law art. 15 A; Infonavit Law art. 29 Bis). It is the same for both returns.
• ICSOE: the extension is written down. The IMSS guidelines for the ICSOE (section 5.5) say that when the last day of the filing period is a Saturday, a Sunday or a non-working day, the period is extended to the next working day. That is why the January 2026 ICSOE could be filed until Monday, January 19.
• SISUB: the rule is not written down. Infonavit's SISUB guide does not say what happens when the 17th is a non-working day. Until it does, our advice is to file on the previous working day. This is a precaution, not a date set by law: filing on the following Monday may turn out to be valid, but nothing in writing guarantees it.

None of this requires waiting until the last day. Filing before the 17th costs nothing and avoids depending on any extension.

What the ICSOE asks for (IMSS)

The basis is article 15 A of the Social Security Law (Ley del Seguro Social, LSS; in Spanish). For each contract in the period reported:

• About the parties: name or registered legal name, Mexican tax ID (RFC), address, contact email and telephone number.
• About the contract: its purpose, its term, and the list of workers who performed the service, with name, CURP (population registry key), social security number and contribution base wage (salario base de cotización), plus the name and RFC of the service recipient for each contract.
• A plain copy of the REPSE registration issued by the STPS (the Ministry of Labor).

What the SISUB asks for (Infonavit)

The basis is article 29 Bis of the Infonavit Law (Ley del Infonavit; in Spanish): general data, service contracts, amounts of housing contributions and loan repayments (aportaciones y amortizaciones), worker information, the calculation of the contribution base wage (salario base de aportación) and a plain copy of the REPSE registration. Infonavit publishes the operational detail (formats and upload) in its Portal Empresarial (employer portal).

Three recurring mistakes

• Filing one and not the other. They are two obligations before two different institutes, with the same deadline. Filing the ICSOE does not discharge the SISUB, and the reverse is also true.
• Reporting the whole workforce in the ICSOE. The ICSOE asks for the workers who performed the service under each contract, not the entire payroll. The SISUB differs in format, not in scope: its worker layout follows the templates of Infonavit's Portal Empresarial and lists, for each two-month period (bimestre), the workers linked to the reported contracts, with pay and contributions as declared in the SUA or SIPARE, the IMSS systems for calculating and paying contributions (source: Infonavit's SISUB user guide, July 2024 version).
• Assuming there is nothing to do without new contracts. The return is filed anyway. The ICSOE accepts the «Sin Información» (no information) type when no contracts were signed in the period, and changes to contracts already reported are communicated with an updating supplementary return (complementaria de actualización). For the SISUB, Infonavit distinguishes the continuing-data report (datos continuos: contracts from an earlier reporting period are still in force and workers are at a third party's disposal, so the three layouts are uploaded) from the no-activity report (sin actividad: no contract in force and no worker at anyone's disposal, so only the REPSE registration and the articles of incorporation (escritura constitutiva) or the tax status certificate (Constancia de Situación Fiscal) are uploaded).

What falls to the client

The provider files these returns, but a failure reaches the client too: the institutes report to the STPS, the REPSE registration can be canceled when the provider stops being up to date, and once the registration is gone the client loses the deduction. If you contract specialized services, confirm every four months that your provider has filed. The verification guide explains how to check the registration; ask the provider directly for the ICSOE and SISUB acknowledgements (acuses).