Your credit card tells the SAT how much you spend: the art. 91 tax discrepancy explained (and how to protect yourself)

Art. 91 of the LISR (the income tax law) is brutally elegant: if in a given year you spend more than you declared you earned, the difference is presumed to be unreported income — and it is on you to prove otherwise. And in case anyone thought spending on plastic doesn't count, the law spells it out in black and white: outlays include credit-card payments, alongside deposits, purchases of goods and investments. Your card statement is, literally, a declaration of expenses that someone else files on your behalf.

How the mathematical trap works

The SAT (Mexico's tax administration) adds up your outlays for the year — deposits in your accounts, acquisitions, investments and payments to your credit cards (data the financial institutions hand over to it) — and compares them against the income you declared. You spent MXN 1.8M, you declared $900k: there is a discrepancy of $900k. The procedure notifies you, gives you a window to explain the source of the funds and, without a sufficient explanation, the difference is assessed as taxable income with an inflation adjustment, late-payment surcharges and a fine — and, for larger amounts and more serious conduct, with the criminal door ajar (an unexplained discrepancy is one of the classic routes to equivalent tax fraud). The key nuance: what counts is the payment on the card, not the purchase — financing a year of living on a credit card and paying it off the next year merely moves the discrepancy to a different tax year.

The four cases that catch honest people

1. "My dad/spouse pays my card." Perfectly legal — and perfectly documentable for what it is: a gift between family members (exempt between spouses and in the direct line, with its informative filing in the annual return if it exceeds $600k together with loans and prizes) or a loan with its contract. Without paperwork, it is your discrepancy. 2. The generous add-on card: the card in your name that the whole family uses concentrates the spending of three people in YOU — against YOUR declared income. 3. Interest-free months as a lifestyle: interest-free installments (meses sin intereses, MSI) do not reduce the outlay, they spread it out — someone living leveraged on plastic with low declared income accumulates a structural discrepancy. 4. The business owner who "pays themselves no salary": they live off the company (endless travel allowances, a personal corporate card, loans that are never repaid) and declare minimal personal income — their visible standard of living against their return is the textbook discrepancy, with deemed dividends for dessert.

The protection: give every peso a birth certificate

A discrepancy is not fought by spending less: it is fought with a documented source. The non-taxable funds that legitimately finance spending — family gifts, loans, inheritances, prizes, exempt sales, your own savings from prior years — are a complete defense if they exist on paper: a contract or certificate, a traceable bank flow, and the art. 90 informative filing submitted on time (omitting it turns a real loan or gift into taxable income by operation of law — the most expensive formal trap in the chapter). The Strategium rule: any tax year where your spending is going to exceed your declared income is documented that year, not when the letter arrives — because the letter arrives with the cross-checks already done.