When to sell bitcoin: decision rules and Mexican taxes

The short answer: sell for a reason, not for a date

Nobody can tell you in advance the best moment to sell bitcoin, and this article does not try. "When should I sell?" usually hides a second question, "is it going up or down?", which has no reliable answer. The useful question is different: what concrete need will the pesos cover?

A sale that answers a reason you had before you looked at the price can be judged on its merits. A sale that answers the mood of the day usually cannot. And if you are a tax resident of Mexico, every sale has a consequence with the SAT (Mexico's tax authority) that is better known before the trade than in April.

Legitimate reasons to sell, and two that are not

• You need the cash. Rent, school fees, a medical bill, a move. Turning savings into spending is not a failure of your thesis.
• You hit a goal. You bought toward a target in pesos (a down payment, for example) and reached it. Selling the part that covers the goal closes a plan.
• Rebalancing. If you decided bitcoin would be a set share of your portfolio and a rally pushed it well above that share, selling the excess brings risk back to the level you chose. Aureo's allocation framework explains how to set that share and when to review it.
• Your thesis changed. You learned something that changes your view of the asset, or of your ability to keep it safe, and you can write it down in one sentence.
• An obligation. A tax bill or a high-interest debt: a financial decision, not a bet on the price.

The two reasons that do not work are panic (selling because the price fell) and euphoria (selling because it rose). Both make the recent price move the reason for the sale, and neither says what the pesos are for.

A four-question decision frame

1. What are the pesos for? If you cannot name where the money goes, you do not have a reason to sell yet; you have a worry about the price.
2. How much do I need, in pesos? The need sets the amount, not your balance. If rent is MX$18,000, you sell MX$18,000 of bitcoin plus the fee, not "half".
3. What does my written rule say? A rule written on a calm day keeps panic and euphoria out of the decision. Example: "If bitcoin goes above 15% of my portfolio, I sell the excess once a year." The discipline in the DCA guide works the same way on the way out.
4. What does selling today cost? The fee, the tax on the gain, and giving up whatever those units do afterwards, in either direction. None of the three stops a sale when the need is real, but all three belong on the table.

Partial sale or full exit

A partial sale covers almost every legitimate reason. A full exit deserves one extra rule: wait a few days and reread your written reason.

What a sale triggers with the SAT (Mexico)

This applies to individuals who are tax residents of Mexico under the law in force as of September 2026. The SAT has published no bitcoin-specific ISR position. What follows summarizes the statute and Prodecon's preliminary, non-binding 2021 reading; use it to prepare questions and ask your accountant which chapter, calculation and duties fit your case. If you also file elsewhere, that system needs a separate review. Aureo's tax guide has the full method.

• Selling is a disposal (enajenación). The Federal Tax Code treats any transfer of ownership as a disposal (art. 14, section I) and the Income Tax Law (LISR) taxes that income (art. 119). Prodecon, the taxpayer ombudsman, concluded in 2021 (an advisory study, not a binding ruling) that cryptocurrency sales "fit the concept of disposal of goods".
• Swapping and spending are disposals too. A barter counts as two disposals (art. 119): trading bitcoin for another asset or paying with it is calculated like a sale for pesos.
• The gain is measured in pesos. Proceeds in MXN minus the updated proven acquisition cost and the fees paid to buy and sell (art. 121, sections I and IV). That is why it matters which units you sell.
• A 20% provisional payment on large sales. For assets other than real estate, art. 126 sets a provisional payment of 20% of the gross amount and assigns withholding or payment according to who the buyer is; the amount exception applies below MX$227,400. The law does not explain how a bitcoin platform applies it. Before selling at or above that amount, ask your accountant who the tax counterparty is and how the provisional payment should be documented.
• The annual return is filed in April. Article 150 sets April of the following year for an individual's annual return. Ask your accountant which income enters, under which chapter, and how any provisional payment is credited; the 2026 progressive tariff runs from 1.92% to 35% under Annex 8 of the RMF.
• If you sell at a loss, articles 121 and 122 expressly describe offsets only for real estate, shares and partnership interests; bitcoin is not on that list. Do not assume either deductibility or the loss treatment: take the calculation and evidence to your accountant. The guide to bitcoin tax losses in Mexico explains the uncertainty.

The SAT has published no crypto-specific income tax guidance, and the OECD list dated 14 September 2026 places Mexico among the countries making their first exchanges under the CARF framework in 2029. Today the burden of documentation is yours.

Records to have ready before you sell

• Date, BTC amount, cost in MXN and fee for each purchase behind the units you are selling, and the method you use to identify those units, applied the same way every year.
• At the sale: date, BTC sent, MXN received, fee, platform, SPEI receipt and the transaction ID on the network.
• Your written rule and the concrete reason for this sale. It is not a tax document, but it prevents the next impulsive one.

Next step

Write your selling rule today, even if you have no plan to sell soon. Estimate the gain on a hypothetical sale with Aureo's tax calculator and take it to your accountant (contador).

When the reason is real, selling bitcoin with Aureo works like this, as of September 2026: you choose the peso amount and the destination CLABE or debit card, send bitcoin from your own wallet (the app where you control your keys) over Lightning, and the pesos arrive by SPEI, usually in under a minute. Custody stays with you until the conversion, there is a single fee (2.00% down to 1.00% depending on size) and your transaction history stays in your account as backup for your return.