Tasa de Interés Interbancaria de Equilibrio — the rate at which Mexican banks lend to each other. Banxico (Mexico's central bank) calculates it every business day. It anchors variable-rate mortgages and many corporate products. When you see «TIIE + 4 points» on a contract, that 4 is the margin the bank charges on top.
Why TIIE shows up on your mortgage contract
Every morning Banxico asks six large banks at what rate they're willing to lend each other pesos. It takes the median, strips out the extremes, publishes the number. That's the TIIE. Sounds technical but the effect is direct: if your mortgage reads «TIIE 28 + 3.5 points», each time that median moves up, your monthly payment the following month moves up too.
It's not the rate you pay — it's the base on which the bank charges you. The gap between TIIE and what you actually pay is called sobretasa or margin, and that's where almost all of the bank's business sits.
TIIE 28, 91 and 182 days — which one applies to you
Banxico publishes three versions depending on the term of the interbank loan:
- TIIE 28 days — the most used. The one you'll almost always see on variable-rate mortgages from BBVA, Santander and Banorte. Moves nearly glued to Banxico's policy rate.
- TIIE 91 days — more common in corporate credit and leasing. Moves slightly slower.
- TIIE 182 days — the least used in consumer products. Shows up in some structured products.
If your contract doesn't say which one, it's 28. What typically happens is that the bank clarifies in parentheses: «variable rate referenced to TIIE 28 days published by Banxico on the first business day of the month».
The real formula: TIIE + margin
A concrete example. BBVA México mortgage over 20 years, variable rate, contractual margin of 3.5 percentage points. If TIIE 28 sits at 10.5%, your annual rate that month is 10.5 + 3.5 = 14.0%. Next month Banxico publishes TIIE 28 at 10.25%, your rate drops to 13.75%. Without you doing anything.
The margin doesn't move — you locked it in on signing day. The only thing that changes is the TIIE.
Banorte and Santander use the same logic. Inbursa too, sometimes on different terms. What changes between banks is the margin: for an A+ profile with BBVA payroll it runs 3.0-3.5pp; for a profile without payroll deposit it can reach 5pp.
If TIIE rises 100 basis points, how much more do you pay?
This matters because Banxico moves the rate in steps of 25 or 50 basis points per meeting. A 100bp rise means four meetings in the same direction.
Mortgage of 1,500,000 pesos over 20 years, margin 3.5pp:
- TIIE 10.5% → rate 14.0% → monthly ≈ $18,650
- TIIE 11.5% → rate 15.0% → monthly ≈ $19,750
Difference: $1,100 a month. $13,200 a year. Over 20 years, if the rate stayed there, that's 264,000 pesos extra. Note: figures are approximate — depends on whether the bank recalculates the monthly payment or the term when TIIE moves. Almost always it recalculates the monthly.
TIIE in 2026: where it is and where it's heading
Mid-2026 TIIE 28 sits around 10.5%. It got there after the cut cycle Banxico started when general inflation returned to the board's target range. The policy rate is at 10.25% and TIIE 28 usually hugs it.
What matters for your wallet isn't the current level but the direction. If the subgovernor talks about sticky services inflation, expect a pause or small hike. If communiques soften, the next cut is on the way.
Banxico's calendar sets meetings every 6-8 weeks. The decision comes out at 13:00 Mexico time on the announced day. If you hold a variable mortgage, that's the day of the month that most affects your next-period payment.
TIIE vs CETES — the difference few explain
The common question: aren't they the same? No.
- TIIE = what banks lend to each other at. Used to set what YOU pay on a loan.
- CETES = what the public lends to the government at. Used to set what YOU earn if you invest in cetesdirecto.
They tend to move in parallel because both follow Banxico's policy rate, but TIIE almost always sits slightly above the CETE for the same term. That small spread is the bank-risk premium.
Does it apply to Kueski, MoneyMan or DiDi Préstamos?
No. And this confuses almost everyone.
SOFOMs E.N.R. — Kueski, MoneyMan, DiDi Préstamos, Credy, Vexi, Binixo — aren't TIIE-referenced. They charge a fixed CAT agreed in the contract, generally high (between 80% and 350%) and offset by the speed of the process. TIIE going up or down doesn't change the cost of a 3,000 peso, 30-day loan with Kueski.
Where it does apply: traditional banks (BBVA, Banorte, Santander, HSBC, Banamex), variable-rate mortgages, corporate credit, leasing. Some regulated SOFOMs E.R. also use it on long-term products.
If it's confusing, here's a simple tell: if your CAT comes in the contract as a fixed number (for example «CAT 154%»), it's not TIIE. If it says «TIIE 28 + X points», it is.
How to check the current TIIE
Three official sources:
- Banxico SIE (Sistema de Información Económica) — the original source. Search «TIIE» and pick the term. Published every business day at 12:00.
- DOF (Diario Oficial de la Federación) — published here with legal value. This is the one that holds in a contractual dispute.
- Bank websites — BBVA and Banorte show the current TIIE for clients. Useful but not the source, it's the mirror.
If your mortgage recalculates at the start of the month, the figure that matters is the TIIE 28 published on the first business day. Not the one from the 15th. Read it in your contract — the clause usually sits in the first three pages.
What typically happens with TIIE in CONDUSEF complaints
Once in a while a complaint shows up at CONDUSEF because the client says the bank applied a different TIIE than the one that corresponded. Almost always it resolves in the bank's favor — because the contract states the exact cutoff date and the client signed it. The exception is when the bank fails to update the rate for months (typical on old mortgages badly migrated to new systems): there the client wins, with refund of overcharged interest.
Common questions
Can I switch my variable-rate mortgage (TIIE) to fixed?
Yes, via subrogación hipotecaria. Another bank takes over your balance and reopens the credit at a fixed rate. Worth it if the spread against current TIIE is wide and you plan to keep the house several years. Process takes 30-60 days and costs between 1% and 2% of the outstanding balance in fees.
Can TIIE be negative?
Theoretically yes, in practice not in Mexico. For that to happen, Banxico's policy rate would have to be near zero — something only seen in Japan and the Eurozone in extreme moments. Not a realistic scenario for the next few years.
If I sign a variable mortgage today and TIIE drops 200bp next year, do they lower it automatically?
Yes. That's the logic of variable. The recalculation is automatic by contract — you don't have to request it. If your monthly didn't drop, call the bank and demand review. It happens that the bank «forgets» to update and nobody claims.
Why does Kueski charge more than a bank if it doesn't use TIIE?
Because it lends to applicants without asking for payroll, without formal Buró, without documented income. You pay for that risk with a high CAT. That's the logic of instant credit.
Does TIIE affect my credit card?
Not directly. The credit-card rate is fixed by contract (or variable referenced to something else, depending on the contract). What does happen: when Banxico raises rates, banks tend to raise their cards' CAT — but it's not automatic and not tied to TIIE.
Where do I check whether my bank applied the right TIIE this month?
Statement plus contract. The statement should say which TIIE it used and from which date. The contract should say which TIIE corresponds. If they don't match, write to CONDUSEF.
Is TIIE de Fondeo the same?
No. TIIE de Fondeo is another rate Banxico started publishing after 2020 as the future replacement for the traditional TIIE. The transition is moving slowly. If your current contract reads «TIIE 28», it's still the traditional one until renegotiated.
And that's it. If your loan is fixed-rate, TIIE isn't your problem. If it's variable, mark Banxico's meetings on the calendar — every 6-8 weeks, Thursday, 13:00. That's the day that counts.