Question: What is the biggest math competition?

List of mathematics competitions

Mathematics competitions or mathematical olympiads are competitive events where participants sit a mathematics test. These tests may require multiple choice or numeric answers, or a detailed written solution or proof.
International mathematics competitions
Championnat International de Jeux Mathématiques et Logiques — for all ages, mainly for French-speaking countries, but participation is not limited by language.
China Girls Mathematical Olympiad (CGMO) — olympiad held annually in different cities in China for teams of girls representing regions within China and a number of other countries as well.
Interdisciplinary Contest in Modeling (ICM) — team contest for undergraduates
International Mathematical Modeling Challenge
International Mathematical Olympiad (IMO) — the oldest international Olympiad, occurring annually since 1959.
International Mathematics Competition for University Students (IMC) — international competition for undergraduate students.
Mathematical Contest in Modeling (MCM) — team contest for undergraduates
Mathematical Kangaroo — worldwide competition.
Mental Calculation World Cup — contest for the best mental calculators
Primary Mathematics World Contest (PMWC) — worldwide competition
Rocket City Math League (RCML) — Competition run by students at Virgil I. Grissom High School with levels ranging from Explorer (Pre-Algebra) to Discovery (Comprehensive)
Romanian Master of Mathematics and Sciences — Olympiad for the selection of the top 20 countries in the last IMO.
Tournament of the Towns — worldwide competition.
Regional mathematics competitions
Asian Pacific Mathematics Olympiad (APMO) — Pacific rim
Balkan Mathematical Olympiad — for students from 15.5 years old from Balkan area
Junior Balkan Mathematical Olympiad — for students under 15.5 years old from Balkan area
Baltic Way — Baltic area
European Girls' Mathematical Olympiad (EGMO) — since April 2012
ICAS-Mathematics (formerly Australasian Schools Mathematics Assessment)
Mediterranean Mathematics Competition. Olympiad for countries in the Mediterranean zone.
North East Asian Mathematics Competition (NEAMC) — North-East Asia
Nordic Mathematical Contest (NMC) — the five Nordic countries
SEAMEO Mathematics Olympiad (SEAMEO) — South-East Asia
South East Asian Mathematics Competition (SEAMC) — South-East Asia
William Lowell Putnam Mathematical Competition — United States and Canada
National mathematics olympiads
Australia
Australian Mathematics Competition
Bangladesh
Bangladesh Mathematical Olympiad (Jatio Gonit Utshob)
Belgium
Olympiade Mathématique Belge — competition for French-speaking students
Vlaamse Wiskunde Olympiade) — competition for Dutch-speaking students
Brazil
Olimpíada Brasileira de Matemática (OBM) — national competition open to all students from fifth grade to university
Olimpíada Brasileira de Matemática das Escolas Públicas (OBMEP) — national competition open to public-school students from fifth grade to high school
Olimpíada de Matemática do Grande ABC (OMABC) — competition for the Grande ABC region
Canada
Canadian Mathematical Olympiad — competition whose top performers represent Canada at the International Mathematical Olympiad
The Centre for Education in Mathematics and Computing (CEMC) based out of the University of Waterloo hosts long-standing national competitions for grade levels 7–12[1][2]
MathChallengers (formerly MathCounts BC) — for eighth and ninth grade students
France
Concours général — competition whose mathematics portion is open to twelfth grade students
Hong Kong
Hong Kong Mathematics Olympiad
Hong Kong Mathematical High Achievers Selection Contest — for students from Form 1 to Form 3
Pui Ching Invitational Mathematics Competition
Primary Mathematics World Contest
Hungary
Miklós Schweitzer Competition
Középiskolai Matematikai Lapok — correspondence competition for students from 9th–12th grade








Indonesia
National Science Olympiad (Olimpiade Sains Nasional) — includes mathematics along with various science topics
Kenya
Moi National Mathematics Contest — prepared and hosted by Mang'u High School but open to students from all Kenyan high schools
Pakistan
Inter School Maths Olympiad — organized nationwide by PakTurk International Schools and Colleges
Saudi Arabia
KFUPM mathematics olympiad – organized by King Fahd University of Petroleum and Minerals (KFUPM).
Singapore
Singapore Mathematical Olympiad (SMO) — organized by the Singapore Mathematical Society, the competition is open to all pre-university students in Singapore.
South Africa
University of Cape Town Mathematics Competition — open to students in grades 8 through 12 in the Western Cape province.
United Kingdom
Most competitions are organised by the UK Mathematics Trust.
The Primary Mathematics Challenge (for primary school pupils) is organised by the Mathematical Association.
The Junior Mathematical Challenge is a multiple-choice competition for students up to year 8 in England and Wales, year S2 in Scotland, year 9 in Northern Ireland.  High scorers in the JMC are invited to compete in the Junior Mathematical Olympiad.
The Intermediate Mathematical Challenge is a multiple-choice competition for students up to year 11 in England and Wales, year S4 in Scotland, year 12 in Northern Ireland.  High scorers in the IMC are invited to compete in the Intermediate Mathematical Olympiad and Kangaroo (for the highest scorers) and in the European Kangaroo (another multiple-choice competition, for other high scorers).
The Senior Mathematical Challenge (formerly National Maths Contest) is a multiple-choice competition for students up to year 13 in England and Wales, year S6 in Scotland, year 14 in Northern Ireland. High scorers in the SMC are invited to compete in the British Mathematical Olympiad.
The UCL Maths Challenge is a competition for Year 6 primary school pupils from London organised by UCL student volunteers.
United States
Generally, registering for these contests is based on the grade level of math at which the student works rather than the age or the enrolled grade of the student. Also normally only competitions where the participants write a full proof are called Mathematical Olympiads.
National elementary school competitions (K–5) and higher
Math League (grades 4–12)
Mathematical Olympiads for Elementary and Middle Schools (MOEMS) (grades 4–6 and 7–8)
National middle school competitions (grades 6–8) AND lower/higher
American Mathematics Contest 8 (AMC->8), formerly the American Junior High School Mathematics Examination (AJHSME)
Math League (grades 4–12)
MATHCOUNTS
Mathematical Olympiads for Elementary and Middle Schools (MOEMS)
Rocket City Math League (pre-algebra to calculus)
United States of America Mathematical Talent Search (USAMTS)
National high school competitions (grade 9–12) AND lower
American Invitational Mathematics Examination (AIME)
American Mathematics Contest 10 (AMC->10)
American Mathematics Contest 12 (AMC->12), formerly the American High School Mathematics Examination (AHSME)
American Regions Mathematics League (ARML)
iTest
Harvard-MIT Mathematics Tournament (HMMT)
High School Mathematical Contest in Modeling (HiMCM)
Mandelbrot Competition
Math League (grades 4–12)
Math-O-Vision (grades 9–12)
Math Prize for Girls
Moody's Mega Math Challenge
Mu Alpha Theta
United States of America Mathematical Olympiad (USAMO)
United States of America Mathematical Talent Search (USAMTS)
Rocket City Math League (pre-algebra to calculus)
National college competitions
AMATYC Mathematics Contest
Mathematical Contest in Modeling (MCM)
William Lowell Putnam Mathematical Competition
Regional competitions