How Mexico elects its 500 federal deputies in 2027

On Sunday 6 June 2027 the whole Chamber of Deputies is renewed: 500 federal seats, for a three-year term, each deputy elected together with an alternate (Constitution, Article 51). It is a midterm election: neither the presidency nor the Senate is up for election. On the same day, at the same polling station, all 32 states hold local elections, including 17 races for governor. There is no judicial election in 2027: an amendment published on 2 June 2026 moved it to 2028.

Mexico’s system is mixed. Part of the Chamber is elected by majority, district by district; the other part in proportion to each party’s nationwide vote. And the Constitution sets two caps so that no party gets too many seats relative to its votes. This is how it works, rule by rule, with the official 2024 figures. The essentials are also in the election guide.

One vote that counts twice

In the election of deputies each voter receives a single ballot (LGIPE, Article 284) and marks one party’s box. That vote is used twice:

• in the district, to elect a first-past-the-post deputy;
• nationwide, added to the votes of the same party, to share out the proportional representation seats.

There is no separate vote for each party’s list, as there is in some countries. People voting outside their precinct at a special polling station, and outside their district but within their state, vote only for the proportional seats.

300 first-past-the-post seats

The country is divided into 300 single-member districts, drawn by dividing the total population by 300; no state may have fewer than two (Constitution, Articles 52 and 53). In each district the candidate with the most votes wins, even without a majority, in a single round. There is no run-off.

200 proportional representation seats

The other 200 seats are filled from each party’s closed lists in five multi-member constituencies of 40 seats each, which group several states. Lists alternate women and men, and the five constituencies are headed by women and men in turn at each election (Article 53).

To take part in this allocation, a party needs two things (Article 54):

• to field first-past-the-post candidates in at least 200 districts;
• to win at least 3% of the valid vote.

The law uses three different vote totals, and they are easy to confuse (LGIPE, Article 15):

• Total vote: every ballot cast.
• Valid vote: the total, minus spoilt ballots and votes for unregistered candidates. This is the base for the 3% threshold.
• National vote: the valid vote, minus the votes of parties below 3% and of independent candidates. This is the base for the allocation and for the caps.

Seats are allocated by the natural quota and largest remainder method (LGIPE, Articles 16 and 17): the national vote is divided by 200, each party receives as many seats as the number of times its votes contain that quota, and any seats left over go to the parties with the largest remainders. Each party’s seats are then distributed among the five constituencies according to its votes in each.

In 2024 the valid vote was 57,209,387, so the threshold was about 1.72 million votes (our calculation: 3% of that figure). The PRD won 1,449,176 votes, 2.53%, and was left out of the allocation. The national vote was 55,688,199, and the natural quota 278,441 votes per seat (agreement INE/CG2129/2024).

The threshold has a second consequence: a national party that does not reach 3% loses its registration (Constitution, Article 41; LGPP, Article 94). That happened to the PRD in 2024. For SOMOS and PAZ, registered since 1 July 2026, 2027 is their first federal election, and the one that will decide whether they keep it.

The two caps

The Constitution limits each party’s seats in two ways (Article 54):

1. No party may have more than 300 seats, counting both kinds.
2. No party may hold a share of the Chamber more than eight points above its share of the national vote. The exception is a party that exceeds that limit through district wins alone: those cannot be taken away.

If a party exceeds a cap, proportional seats are taken from it until it fits, and they are shared among the others (LGIPE, Article 17).

The caps apply to each party, not to each coalition. So it matters to which party each district won by a coalition is counted. In 2024 the INE did not simply follow the coalition agreements: it counted each win for the party to which the winner belonged when the agreements were registered, the so-called “effective membership” (agreement INE/CG645/2023).

How it was applied in 2024. Morena won 43.60% of the national vote. Adding eight points, 51.596%, its limit was 257.98 seats out of 500, which the INE set at 257. By effective membership, the INE credited it with 182 district wins, and the first allocation gave it 87 proportional seats: 269 in all, 12 above the cap. It was given 75 instead of 87, and the remaining 125 seats were shared among the PAN, the PRI, the PT, the PVEM and Movimiento Ciudadano. No other party reached its limit (recitals 66 to 68 of the agreement). The Electoral Court of the Federal Judiciary upheld the allocation on 28 August 2024 (case SUP-REC-3505/2024 and joined cases).

Coalitions

Parties can field a joint candidate in each district. The law provides for three kinds of coalition (LGPP, Article 88): full, covering every candidacy; partial, at least half; and flexible, at least a quarter. A coalition changes the district candidacy, not the ballot or the proportional allocation:

• On the ballot, each party appears with its own logo, even in a coalition (LGPP, Article 87). You vote for a party.
• The votes of coalition partners are added up for the joint candidate in the district, and each counts for its own party in the proportional allocation.
• If you mark two or more parties of the same coalition, the vote counts once for the candidate and is split equally among those parties (LGIPE, Article 311). If you mark parties that are not in a coalition, the vote is spoilt (Article 288).

Newly registered parties cannot form coalitions before their first election (LGPP, Article 85): SOMOS and PAZ will run alone in 2027. Coalition agreements must be filed with the INE no later than thirty days before the pre-campaigns (LGPP, Article 92), around early December 2026. Morena, the PVEM and the PT have announced that they will run together; coalitions are only final once the INE registers their agreements.

Re-election

The constitutional amendment published on 1 April 2025 bars deputies from being re-elected for the following term (Article 59). But its third transitional article says that the ban applies from the 2030 elections. As a result, in 2027 sitting federal deputies may still seek immediate re-election, under the previous rules.

The 2027 calendar

The INE’s General Council approved the 2026-2027 federal electoral plan and calendar on 30 July 2026 (agreement INE/CG479/2026). Some dates are set by law; others by the INE calendar, which we know from press reports and will check against the official document.

On election night the INE publishes preliminary results, but the official ones come from the district counts. Mexicans abroad cannot vote for federal deputies.

The 2024 results

These are each party’s votes in the election of deputies of 2 June 2024, according to the INE agreement that allocated the proportional seats. The percentage is of the valid vote, the base for the 3% threshold.

There were also 2,189,171 spoilt ballots (3.68% of the total vote of 59,447,863) and 49,305 votes for unregistered candidates. In 2024 Morena, the PVEM and the PT ran in the “Sigamos Haciendo Historia” coalition, and the PAN, the PRI and the PRD in “Fuerza y Corazón por México”; Movimiento Ciudadano ran alone.

With those votes, the INE made up the Chamber as follows in August 2024. District wins are counted here by the party that nominated each candidate under the agreements, as in the agreement’s final table; the last column compares the share of seats with the share of the national vote, the base for the eight-point cap (our calculation).

No party exceeded its own cap. Together, the three “Sigamos Haciendo Historia” parties held 364 seats, 72.8% of the Chamber, with 58.40% of the national vote; the “Fuerza y Corazón por México” parties held 108 seats, 21.6% (our calculation from the agreement’s data). Because the caps apply party by party, they do not limit what a coalition adds up to: that was at the heart of the debate over the 2024 allocation. Constitutional amendments require the votes of two thirds of the deputies present, as well as the Senate and a majority of the state legislatures (Article 135).

Today’s Chamber is not exactly the one elected in 2024: some deputies elected for one party sit in another party’s parliamentary group. As of 24 October 2026, the groups are Morena 254, PAN 69, PVEM 61, PT 49, PRI 36, Movimiento Ciudadano 30 and one deputy with no party, according to the Chamber’s Legislative Information System.

What it means for the test

In 2027 there are eight parties with national registration with the INE: Morena, the PAN, the PRI, the PVEM, the PT, Movimiento Ciudadano, SOMOS and PAZ. The test compares your answers with each of them separately, even if they run in a coalition: on the ballot you vote for a party, and each party has its own platform and its own positions. The test does not measure how many seats each would win or which candidate in your district your vote would help.

Each party’s positions, with their sources, are on the party pages and in the party comparison. How the result is calculated is explained in “How your affinity is calculated”, and who the eight parties are in “Mexico’s political parties”. To find out which one you agree with most, take the test.