Annual tax return for corporations in Mexico 2026: complete guide for SA de CV

Who must file the annual corporate return

Every legal entity (persona moral) with activities in Mexico during the fiscal year must file an annual ISR return with SAT. This includes without exception Sociedades Anónimas de Capital Variable (SA de CV), Sociedades de Responsabilidad Limitada (S de RL), Sociedades por Acciones Simplificadas (SAS), Asociaciones Civiles (AC) and Sociedades Civiles (SC). The obligation exists even if the company had zero income during the year — in that case you file a zero-income return, but you do file.

The only relevant exception is companies under the Simplified Trust Regime for legal entities (RESICO PM), introduced in 2022. These have different calculation rules, though the March 31 deadline still applies. If your company is in RESICO PM, the rates and framework in this guide do not apply directly.

The calculation base: what is taxable profit (utilidad fiscal)

Corporate ISR in Mexico is applied to taxable profit (utilidad fiscal), which is not the same as the accounting profit that appears in your financial statements. The gap between the two is precisely where most mistakes happen — and where tax-experienced accountants generate the greatest savings.

The legal formula under article 9 of the LISR is:

The difference between cumulative income and accounting income comes from timing rules — SAT may require you to accrue income before your accounting registers it as earned — and from items your accounting books record as income but SAT does not consider cumulative. The same applies in reverse for deductions: many accounting expenses are not fiscally deductible because they fail the requirements of article 27 of the LISR.

Authorized deductions: the exact requirements that cannot be ignored

Article 27 of the LISR sets out the requirements that every deduction must meet to be fiscally valid. The most expensive to overlook is the materiality requirement: SAT requires documentary evidence that the transaction actually occurred — beyond the CFDI. Contracts, service orders, delivery evidence, emails, bank transfers. Since 2020, SAT has intensified audits focused on simulated non-existent transactions (EFOS/EDOS), and the consequences of a supplier being retroactively classified as an EFOS can invalidate deductions from prior years.

The basic formal requirements every deduction must meet: it must be backed by a valid CFDI with all fields correct, the expense must be strictly necessary for the business activity (art. 27 section I), it must be recorded in the books, if over $2,000 MXN it must have been paid by bank transfer or cheque (not cash), and it must be correctly linked to the supplier's RFC in the payment complement if not paid immediately.

PTU and its impact on the ISR calculation

Employee profit sharing (PTU) is deducted from the taxable profit of the year it is paid, not the year it corresponds to. This creates an asymmetry: if your company generated profits in 2025 and paid PTU in May 2025, that PTU is deducted in the 2025 annual return (filed in March 2026). But if for any reason you paid it in January or February 2026 after closing the 2025 books, it is technically deductible in fiscal year 2026 — not 2025.

This timing detail is one of the most frequently misapplied points in small and medium-sized companies.

Monthly provisional payments during the year: the utility coefficient

The annual return is not a single payment in March — it is the final settlement of a monthly provisional payment system the company made throughout the prior year. Understanding this is key to avoiding surprises in March.

Provisional payments are calculated by applying the utility coefficient (coeficiente de utilidad) from the prior year to the cumulative income of the period. The utility coefficient is simply the prior year's taxable profit divided by its cumulative income. If your company had taxable profit of $500,000 on income of $2,000,000, your coefficient is 0.25 — meaning SAT assumes you generate 25 cents of taxable profit for every peso of income.

If provisional payments exceeded the annual ISR, you have a balance in your favor that can be offset against future payments or requested as a refund. Many companies that had a worse-than-expected year — lower income, extraordinary expenses — reach March with a balance in their favor without knowing it, simply because no one ran the projection in time.

Prior year tax losses

If your company had tax losses in prior years that you have not fully amortized, you have the right to apply them against 2025 taxable profit. Article 57 of the LISR allows carrying forward tax losses for up to ten fiscal years following the year they were generated, updated by the inflation factor.

This right is permanently lost if not exercised within ten years, and it is not transferable between companies in the same group. In a review we carried out for a client with three years of accumulated unamortized losses, correctly applying them produced a tax saving of $218,000 MXN in a single year. The mistake was not intentional — no one had been maintaining an updated record of the pending loss balance.

How to file: the SAT portal and e.firma

The corporate annual return is filed exclusively online through sat.gob.mx under "Declaraciones" → "Presentación de declaración anual de personas morales". The system automatically pre-loads information from issued and received CFDIs, payroll and reported provisional payments.

Filing requires the e.firma of the legal entity — not the personal one of the legal representative, but the one linked to the company's RFC. This is another point where many companies get blocked in March: the corporate e.firma expired and renewing it requires the representative's personal one, which may also have expired.

What happens if you do not file or file late

The fine for not filing the annual return on time ranges from $1,810 to $44,790 MXN per omission (article 82 CFF, 2026 updated amounts). If there is also ISR due that was not paid, a 1.47% monthly surcharge on the unpaid tax and an inflation adjustment are added. SAT fines are reduced by 50% if you file the omitted return voluntarily before SAT formally requires it.

A scenario we see more often than it should happen: the legal representative of an SA de CV files their personal annual return in April, convinced they have fulfilled all obligations, unaware that the company's was due a month earlier. By the time they receive the requirement via tax mailbox, two months of surcharges have already accumulated.

Companies with foreign shareholders: additional considerations

If you are a foreigner who opened a company in Mexico, the annual return triggers two additional layers. The first is the CUFIN (Net Fiscal Profit Account): a mandatory record that determines which portion of dividends you distribute has already paid corporate ISR and which has not. Distributing dividends without an up-to-date CUFIN creates double taxation that is perfectly legal to avoid with correct record-keeping.

The second is dividend withholding: if your SA de CV distributes dividends to individual shareholders in 2026, an additional 10% ISR withholding applies on the distributed amount (article 140 LISR). This 10% is creditable for the individual shareholder in their own annual return, but if it is not correctly withheld and remitted, the company is jointly and severally liable.

Additionally, as a tax resident of Mexico, your personal tax position and your company's are intertwined. The annual return of the company directly affects what you declare personally — especially if you receive salary from it, which is a common and efficient structure when done correctly.