Among the 4 largest banks, fundamental capital ranks them differently from the capitalization ratio
MEXICO · FINANCIAL SYSTEM
An InsightIA note · September 2026 · figures as of July 31, 2026 · reissue of October 12, 2026
At the end of July, the capitalization ratio of the 4 largest banks ranges from 19.3% to 24.4%, and their fundamental capital ratio from 12.7% to 18.8%.
What changed
On September 18, 2026, the Comisión Nacional Bancaria y de Valores [CNBV] (National Banking and Securities Commission) published the capitalization indicators of commercial banks, with figures as of July 31, 2026, in its Comunicado No. 20 (Press Release No. 20) [V]. The capitalization ratio of commercial banks as a whole stood at 20.8%, with a basic capital ratio of 18.7% and a fundamental capital ratio of 17.2% [D]. All institutions were placed in category I of the early warning system [V]. Banco de México reported those figures to the Commission on September 10, 2026, based on information from the institutions themselves [V].
What it reveals
Among the 4 largest banks by assets [D], which hold 55.5% of the total assets of commercial banks [D], the 2 indicators rank the banks in different orders: the 2 sequences diverge from second place onward [D].
The Disposiciones de carácter general aplicables a las instituciones de crédito (General Provisions Applicable to Credit Institutions), the rules with which the CNBV regulates banks, separate the 2 measures into 2 sections of the same article [V]. Their article 1 defines the capitalization ratio as net capital divided by risk-weighted assets [V]. It separately defines the fundamental capital ratio, which divides only fundamental capital, the capital in section I of article 2 Bis 6, by those same assets [V]. The minimum capitalization ratio is 8%, and the minimum fundamental capital ratio is 4.5% [V]. The Provisions also require a conservation buffer of 2.5% of risk-weighted assets, which must be made up of fundamental capital [V].
For whoever allocates capital, the consequence is arithmetic. Among these 4 banks, the distance between the 2 ratios within a single institution ranges from 3.55 to 9.04 percentage points, against 3.59 for commercial banks as a whole [D]. The same capitalization ratio can support 2 very different amounts of fundamental capital headroom, and fundamental capital is what covers the buffer [D]. The mismatch predates July: at the end of June, the largest gap was 8.94 percentage points [D].
Our hypothesis is that current practice reads the headroom allocated among businesses in the capitalization ratio, the one in the title of the press release [H]. What that reading fails to see is that the same ratio supports different amounts of fundamental capital headroom, and that the buffer is made up of that capital [D]. Structured as a Decision System, Capital Allocation would allocate capital against the ratio that binds first at each bank, rather than against the one that heads the press release [H]. A committee that already calculates its available capital on the basis of fundamental capital would refute the hypothesis.
Which decision is affected
Who decides: the committee that allocates capital among businesses
What they decide: how much capital to assign to each business, and with what return hurdle
What changed in that decision: their criterion, namely which of the 2 ratios measures the headroom being allocated
The capitalization ratio describes solvency as the supervisor sees it [D]. The conservation buffer is made up of fundamental capital [V], so the headroom that limits allocation may be that of the ratio that does not head the press release [H]. This week, the committee can review which of the 2 ratios it uses today to calculate the available capital it allocates among businesses. It can also review what happens to each business's return hurdle if the calculation uses the other ratio.
The question
How much available capital disappears if headroom is measured with the fundamental capital ratio?
Sources
CNBV, Comunicado No. 20 of September 18, 2026, "Índice de Capitalización de la banca múltiple al cierre de julio de 2026" (Capitalization ratio of commercial banks at the end of July 2026) · https://www.gob.mx/cnbv/prensa/indice-de-capitalizacion-de-la-banca-multiple-al-cierre-de-julio-de-2026
CNBV, Indicadores de capitalización (Capitalization indicators), file ICAP_BM_202607.pdf, Portafolio de Información (Information Portfolio), Banca Múltiple (Commercial Banks) · https://portafolioinfo.cnbv.gob.mx/PortafolioInformacion/ICAP_BM_202607.pdf
CNBV, Disposiciones de carácter general aplicables a las instituciones de crédito, article 1, sections XXXIII, XXXIV, and LXXX, and article 2 Bis 5 · https://www.cnbv.gob.mx/Normatividad/Disposiciones%20de%20car%C3%A1cter%20general%20aplicables%20a%20las%20instituciones%20de%20cr%C3%A9dito.pdf
CNBV, Boletín Estadístico de Banca Múltiple (Commercial Banks Statistical Bulletin), July 2026 close, file BE BM 202607.xlsx, sheet "EF Resumen", row ACTIVO · https://portafolioinfo.cnbv.gob.mx/Paginas/Contenidos.aspx?ID=40
Evidence markers: [V] verified against a primary source · [D] derived · [H] hypothesis. The supporting evidence book, with 1 row per unit of claim, is kept in this piece's file.
No institution is named. The intervals correspond to the 4 largest banks by total assets, according to the Statistical Bulletin for the end of July 2026. The endpoints of an interval of 4 are values of a single institution and can be recovered from the public table, so the note is pseudonymous rather than anonymous.
Figures in the text are rounded to 3 significant digits [D]. The CNBV publishes the ratios with 2 decimal places, and the differences were calculated from those published figures.
Which ratio each bank uses to calculate its available capital is internal information, which is why the note's 3 [H] are published as hypotheses with their discriminator.
This note reissues the one published on September 23, 2026. It retains the event, the figures, the sources, and the supporting evidence book, and adds the Decision Systems function to which the decision belongs and the improvement hypothesis that follows from it.