Mexico's Chamber of Deputies mixes 300 single-member districts, won by plurality
(mayoría relativa, MR), with 200 list seats shared by national vote
(representación proporcional, RP). A cap on over-representation is meant to stop any
party turning a plurality of votes into a much larger share of seats. On 2 June 2024 Morena and its
allies won 58.4% of the
votación nacional emitida and 364 of 500 seats, more than the 334 needed to amend the Constitution.
Seat lab · INE's official 2024 and 2021 figures
Change one rule, watch the Chamber move.
Set the rules yourself
district (MR) list (RP)
Valid vote
—
Threshold
—
Cociente natural
—
Majority · two thirds
—
Party
Vote
MR
RP
Seats
Seat share
Limit
vs official
The full trace, step by step
Votes, district winners and both MR counts: INE/CG2129/2024 and
INE/CG1443/2021. With the law as applied the lab returns the official
allocation for every party and circunscripción.
300 deputies are elected in single-member districts, by plurality. 200 are elected from closed lists in five
regional circunscripciones of 40 seats each. Every voter casts one ballot: the vote for a
district candidate also counts for that candidate's party list. Deputies sit for three years.
A party must run candidates in at least 200 districts and win at least 3% of the
votación válida emitida (the total less null votes and votes for non-registered
candidates): 57,209,387 valid votes in 2024, so 1,716,282 were
needed. The PRD won 2.53%: it took no list seats, kept the district it won, and lost its
national registry.
The votación nacional emitida is the total less the votes of parties under 3%, of independent
candidates, of non-registered candidates and null votes: 55,688,199. Each qualified
party's share of it decides its list seats and its cap.
The national vote divided by 200 gives the cociente natural, 278,441 votes. Each party
gets one seat per whole quota; seats left over go to the largest remainders (resto mayor).
No party may hold more than 300 seats in all, nor a share of seats more than 8 points above its share of the
national vote. The exception: seats it won in districts are never taken away. INE takes the integer part, so
Morena's 43.60% plus 8 points of 500 seats is 257.
Coalition partners stand joint district candidates, and the coalition agreement assigns each district to one
party (the siglado). Since 2021 INE counts a district for the caps by the winner's effective
party affiliation instead (INE/CG193/2021, INE/CG645/2023). For Morena that is 182 districts, against
161 under the agreement: with 87 list seats it would hold
269, so it keeps 75.
Party
MR (agreement)
MR (affiliation)
First pass RP
Limit
Over by
Morena
161
182
87
257
12
PAN
32
31
36
130
—
PRI
9
10
24
99
—
MC
1
1
23
98
—
PVEM
57
40
18
84
—
PT
38
34
12
69
—
6 · Sharing the rest · LGIPE art. 18, CPEUM art. 54 VI
The capped party's votes are taken out, leaving the votación nacional efectiva,
31,410,242. The other 5 parties share the remaining
125 seats on a new quota of 251,282:
PAN 40, PRI 26, MC 26, PVEM 20, PT 13.
7 · Into the five circunscripciones · LGIPE arts. 17.3, 18.2, 19
A capped party spreads its seats by its own quota of votes per seat; the others by each circunscripción's vote
over its seats still to fill. Leftovers go by largest remainders, parties taking turns in order of national vote
(INE/CG645/2023).
List seats by circunscripción · 2024
Five regions, 40 seats each.
1 · Guadalajara, Jalisco
2 · Monterrey, Nuevo León
3 · Xalapa-Enríquez, Veracruz
4 · Mexico City
5 · Toluca de Lerdo, State of Mexico
The five circunscripciones (2023 distritación, INE/CG130/2023) · Distritación federal 2023: Instituto Nacional Electoral (INE), Cómputos Distritales 2024
Circunscripción 4 Mexico City, Guerrero, Hidalgo, Morelos, Puebla, Tlaxcala
Circunscripción 5 Colima, State of Mexico, Michoacán, Querétaro
2024 · INE/CG2129/2024 and SUP-REC-3505/2024
58% of the vote, 73% of the seats.
Morena, PT and PVEM ran in 2024 as the coalition Sigamos Haciendo Historia. Candidates of the
three won 256 of the 300 districts. Under the coalition agreement Morena had 161 of them,
PVEM 57 and PT 38. Votes marked for more than one coalition party
were divided among them, so each party had its own national vote, and the 8-point test was run on each party
separately. Only Morena reached its limit. The PVEM (9.0% of the national vote) and the PT were far from theirs, and kept their list seats.
The opposition parties argued before INE and the Electoral Tribunal that the cap should apply to the coalition as
a whole. INE's Consejo General allocated the
seats on 23 August 2024 as in the lab's first preset. On 28 August 2024 the Tribunal's Sala Superior
confirmed it, 4 votes to 1 (SUP-REC-3505/2024): the
tribunal held that art. 54 sets the limits for each party.
By effective affiliation the same 256 districts split Morena 182, PVEM 40, PT 34.
Counting by the agreement instead would have left Morena under its limit: 373 for the coalition, as with no cap at all.
Rule
Morena
PVEM
PT
Coalition
Two thirds
2021
As allocated
236
77
51
364 / 500
yes (334)
278 / 500
Cap per coalition
218
69
45
332 / 500
no (334)
278 / 500
MR by party of origin
248
75
50
373 / 500
yes (334)
278 / 500
No cap
248
75
50
373 / 500
yes (334)
278 / 500
100 RP seats
185
69
46
300 / 400
yes (267)
231 / 400
Pure PR of 500
218
45
29
292 / 500
no (334)
239 / 500
Coalition: Morena + PT + PVEM, as elected. 2021 column: Juntos Hacemos Historia, the same three
parties, on the 2021 votes. In 2021 no party reached its limit, so the cap rules change nothing that year:
278 of 500.
Each of the 31 states and Mexico City elects three senators. The slate with the most votes takes two seats; the
third goes to the first name on the slate of the party that came second (primera minoría).
Another 32 are elected from national closed lists, by cociente natural and resto mayor on the national vote, for
parties with at least 3% of the total list vote. The Senate has no over-representation cap. Senators sit for six
years.
In 2024 Sigamos Haciendo Historia won 29 entities, Fuerza y Corazón por México 2 and Movimiento Ciudadano 1. With 32 list seats,
Morena, PT and PVEM were elected to 83 of 128, 3 short of the 86 for two thirds. On 28 August 2024 the two PRD senators-elect, Araceli Saucedo and José Sabino Herrera, joined Morena's group (85). The judicial reform passed the Senate on 11 September 2024 by 86 to 41 with the vote of PAN senator Miguel Ángel Yunes Márquez.
Sigamos Haciendo Historia (Morena, PT, PVEM)
Fuerza y Corazón por México (PAN, PRI, PRD)
Movimiento Ciudadano
Senate 2024: slate that won the two majority seats in each entity · Distritación federal 2023: Instituto Nacional Electoral (INE), Cómputos Distritales 2024
Party
List vote
State
List
Seats
State seats by party of origin of each formula; list votes and allocation: INE/CG2130/2024.
With 96 seats, two thirds is 64.
The 2026 electoral reform
Proposed, rejected, then Plan B.
The initiative of 4 March 2026
Replace the 200 list deputies: 100 for best-placed district losers and 100 by party vote in five constituencies, with seats for Mexicans abroad
Abolish the 32 national-list senators
Cut electoral spending by about 25%; reduce party broadcast time from 48 to 35 minutes a day
Regulate AI and bots in campaigns; electronic voting; restructure INE and the OPLEs
Rejected in the Chamber of Deputies on 11 March 2026:
259 for, 234 against,
1 abstention; 334 were needed.
PT and PVEM, Morena's allies, voted against; the first initiative of the President rejected by Congress. CNN (secondary) ↗
Plan B, published 23 April 2026
Art. 115: ayuntamientos of a municipal president, one sindicatura and at most 15 regidurías, from each municipality's next term
Art. 116: state congress budgets capped at 0.70% of the state budget, from the next legislature; no real increases where already below
Art. 134: pay of INE, OPLE and electoral-tribunal officials capped at the President's (art. 127); no private medical, life or pension insurance
Transitorio 3: Senate budget cut 15% in real terms over four fiscal years from 2027
Dropped in the Senate on a PT reservation: changes to art. 35 that would have allowed the recall vote in 2027
Senate 25 March 2026; Chamber 8 April 2026,
377–102; in force 24 April 2026.
DOF decree ↗
Unchanged for 2027
Chamber of 500 (300 + 200 PR in five constituencies), 3% threshold, 8-point and 300-seat caps
Senate of 128 with 32 national-list seats
INE structure and Consejo General of 11; OPLEs remain
Public party funding formula (art. 41 II)
PREP
The labs' "100 RP seats" and "none" (Senate) options show the size of those proposals on the 2024 votes. The
initiative's 100 seats for best-placed district losers cannot be modelled from party totals, so the Chamber
option halves the list tier instead.