OMO Contest Information

The Fall 2019 Contest will be held from October 25 - November 5, 2019.
The Spring 2020 Contest will be held from March 20 - 31, 2020.


Please send any questions or suggestions to

Registration Instructions

  1. Gather a team of up to four students. No student can be on more than one team. Starting Fall of 2019, we no longer require that all students must not have graduated from high school.
  2. Designate a team leader, who will submit answers on behalf of his or her entire team. The team leader will need an account on the site. Click here to register an account if you don't already have one.
  3. The team leader will submit answers to the contest through his or her individual account on Note that this is different from previous years!
  4. The team leader will also be asked to input a team name and the names of all the team members.

The contest can be found under Contests & Rules, alongside all the NIMO contests. Click the link labelled "Register/Update Team" to input the names of your team members.

The change from a team account to a single individual account saves students from having to create a new account each year, without the hassle of having each student create an individual account.

Note: when we say up to four students, we really do mean "up to"! Because the time limit is so long, partial teams are not significantly disadvantaged, and we welcome their participation.

Contest Format

  • The Fall and Spring contests consist of 30 problems each.
  • Each answer is a nonnegative integer not exceeding 231-1 = 2147483647.

During the testing windows, teams may work on the problems as much as they like. The problems are sorted roughly in order of difficulty and range from early AMC- to late IMO-level.

Team Guidelines

Students may compete in teams of up to four people, but no student may belong to more than one team. Starting Fall of 2019, we no longer require that all students must not have graduated from high school. Only one member, namely the team leader, on each team needs an account. Please see the registration instructions for more information.

Each team will submit its final answers through its team account on the submission form. Since the current interface does not allow for much flexibility in communication between team members, we recommend using Google Docs and Spreadsheets or Private AoPS Forums to discuss problems and compare answers, especially if teammates cannot communicate in person. Teams may spend as much time as they like on the test before the deadline.

Teams need not remain the same between the Fall and Spring contests, and students are permitted to participate in whichever contests they like.


  1. Four-function calculators (calculators which can perform only the four basic arithmetic operations) are permitted on the Online Math Open. Any other computational aids, including scientific calculators, graphing calculators, or computer programs, are prohibited. All problems on the Online Math Open are solvable without a calculator. Four-function calculators are permitted only to help participants reduce computation errors.
  2. Drawing aids such as graph paper, ruler, and compass are permitted. However, electronic drawing aids, such as Geogebra and graphing calculators, are not allowed. Print and electronic publications are also not allowed.
  3. Members of different teams may not communicate with each other about the contest while the contest is running.
  4. Anything that may be considered offensive or inappropriate is not allowed as a team name.
  5. Team member names must be the actual team members' names. In particular, names of other people (including celebrities) or phrases that do not represent actual people are not allowed. This includes names of mathematical objects and multiple names concatenated into one name entry.
  6. At our discretion, we may rename teams or team members that do not satisfy these rules.
  7. Your score is the number of questions answered correctly; that is, every problem is worth one point. Ties will be broken based on the "hardest" problem that a team answered correctly. Remaining ties will be broken by the second hardest problem solved, and so on. (Problem m is harder than problem n if fewer teams solve problem m OR if the number of solves is equal and m > n.)
  8. Participation in the Online Math Open is free.

Clarifications and Results

Clarifications will be posted as they are answered. For the most recent contests, they will be posted here. If you have a question about problem wording, please email with "Clarification" in the subject. We have the right to deny clarification requests that we feel we cannot answer.

After the contest is over, we will release the answers to the problems within the next day. Please do not discuss the test until answers are released. If you have a protest about an answer, you may send an email to (include "Protest" in the subject). Results will be released in the following weeks.

Note: Results will be counted only for teams that submit answers at least once. Teams that only register an account will not be listed in the final rankings.