What is the difference between AACOMAS and AMCAS?

Dear Applicant,

Two different organizations run AMCAS and AACOMAS. The AAMC describes AMCAS as "the AAMC's centralized medical school application processing service." AACOM describes AACOMAS as "the centralized online application service for U.S. colleges of osteopathic medicine." Same job, different owners, and a handful of rules that quietly diverge.

AMCAS is operated by the AAMC, the Association of American Medical Colleges. The AAMC says "Most U.S. medical schools use the AMCAS program as the primary application method for their entering classes," and that "The AMCAS program is only available to the first-year entering classes at participating U.S. medical schools."

AACOMAS belongs to the American Association of Colleges of Osteopathic Medicine, which says of its service: "We verify your application for accuracy, process it and send it with your materials to those osteopathic medical schools you designate." Its applicant help center states that "All accredited US osteopathic medicine programs" participate, with two exceptions, UNTHSC-TCOM and Sam Houston State University College of Osteopathic Medicine, whose applicants "must use the separate Texas Medical and Dental School Application Service."

Texas is one place where the two systems rhyme. The AAMC: "To apply to an MD program at a public medical school in Texas, you will need to apply using the Texas Medical and Dental Schools Application Service (TMDSAS)."

AACOMAS publishes a dated table. Its first row reads: "The AACOMAS application cycle opens. May 4, 2026." The cycle closes "August 2, 2027 at 11:59 PM ET," and "All application processing ends. August 5, 2027 at 5 PM ET."

Its two owners publish two different close dates, so work to the earlier one. The August 2 table above is on the AACOMAS applicant help center, run by Liaison, which operates the service. AACOM, the association that owns it, says something else on its own page explaining the application: "The AACOMAS application cycle for 2026-2027 ends on April 30, 2027!" and, under Key Dates, "April 30, 2027: Last day for AACOMAS application submissions to be completed." Further down that same AACOM page sits a third framing: "The application cycle runs from May to the following June."

We are not reconciling those for you, because only your programs can. What makes the conflict survivable is the rule both sides repeat: the program's deadline is the one that binds. AACOMAS puts it as "In some instances, the individual program's deadline may differ from the application's cycle dates." AACOM's own program listings carry a date directly, as Des Moines University's does with "Primary Application Deadline: April 30, 2027." Look up every program on your list and treat the earliest date you find as your real one.

AMCAS opened one day later. The 2027 AMCAS Application Workbook says: "Beginning May 5, 2026, you may initiate your 2027 AMCAS application at www.aamc.org/amcas."

AMCAS leaves deadlines to the schools. The AAMC: "All application deadlines are set by individual medical schools," and "Your application must be submitted to the AMCAS program (not processed) by 11:59 p.m. ET to meet the deadline." AACOMAS publishes its own cycle dates and notes that a program's date can differ from them: "In some instances, the individual program's deadline may differ from the application's cycle dates." Either way, "You can submit your application up until 11:59 PM ET on the deadline date."

AMCAS: "The 2027 application fee is $180 for the first school and $48 for each additional school."

AACOMAS: "AACOMAS charges $198 for the first program you apply to and $60 for each additional program."

Fee help is one place the two differ. The AAMC's Fee Assistance Program provides a "Waiver for all AMCAS application fees for one (1) submission, covering up to 20 medical school submissions ($1,092 value), submitted by Dec. 31, 2027." AACOMAS waivers are narrower, and limited in number: "Each fee waiver covers only the initial application fee, so if you wish to apply to additional programs, you are responsible for the remaining balance." They go out in "a limited number" and "on a first-come, first-served basis," and "You must request a fee waiver before you submit your application. Requests received after an application has been submitted will not be honored."

On repeated courses the two services say the same thing. AMCAS: "The AMCAS program counts grades for all attempts of a repeated course, even if your school does not." AACOMAS: "AACOMAS does not recognize an individual school's policies for forgiveness, academic renewal, or grade replacement for repeated courses," and "All grades earned for repeated courses are factored into your AACOMAS School GPA."

AMCAS adds a step for forgiveness policies. If a school replaced an original grade with a special transcript symbol, "the original grade and attempted credits must be entered on your AMCAS application, regardless of whether they appear on your official transcript." Leave it out and "the AMCAS program will return your application to you to enter the original grade, which may cause you to miss application deadlines and forfeit fees."

A difference that is easy to miss is where the math lives. AMCAS: "The BCPM GPA is comprised of Biology, Chemistry, Physics, and Mathematics courses. All other coursework will be calculated in the AO (All Other) GPA." AACOMAS divides each year into "Science, Non-Science, and Total (science plus non-science) sections." Its science list is "Biochemistry, Biology/Zoology, Inorganic Chemistry, Organic Chemistry, Other Sciences, Physics." Its non-science list is "Behavioral Sciences, English, Mathematics, Other Non-Science." The same calculus grade sits inside the science GPA on one application and outside it on the other.

Credit hours convert differently too. AACOMAS states a fixed ratio: "AACOMAS calculates all GPAs in semester hours. Courses that were completed in quarter hours are converted to semester hours. The conversion ratio is 1.0 quarter hour = 0.667 semester hours." AMCAS says your application "will automatically convert most undergraduate credit hours (also known as units and hours) to either semester hours or supplemental hours based on conversions provided by undergraduate institutions."

AACOMAS does not go and get it. Its help center puts the job on you in plain words: "It is your responsibility to request MCAT scores be sent to AACOMAS and follow up on any missing MCAT scores in a timely manner." The request has a date attached: "On or after May 4, 2026, you must request that all MCAT scores be sent to AACOMAS for the 2026-2027 application cycle. If you sent your scores to AACOMAS in a previous cycle, you must re-send them." A reapplicant's old request does not carry forward, and the page says so twice: "Scores sent in previous application cycles will not be posted to your application."

Two things have to be in place before a score can attach. Inside the application: "If you took or registered to take the MCAT exam, enter your AAMC ID number in the MCAT Scores page. Additionally, enter your date of birth in the Biographic Information section. You must list this information before your official scores can be matched to your application." Then at the other end: "Go to AAMC and request your scores be released to AACOMAS." AACOMAS adds that paper will not do, and that the posting is not instant: "After AAMC processing, scores are sent to AACOMAS in batches and then posted to applications daily."

There is a published interval after which a missing score is worth chasing: "If your scores are not posted at least five weeks after your test date, contact AAMC to confirm that your MCAT scores were sent to AACOMAS on or after May 4, 2026." Watch which deadline governs that chase. Official test scores are matched to an AACOMAS application only through "August 3, 2027 at 5 PM ET," and the cycle dates page tells you why to move early: "Be sure to request your transcripts and official test scores in advance so they are received by this date."

None of the AAMC pages fetched for this article state whether an AMCAS applicant has to make the same request, so this is not a claim about which service is easier. It is one sourced rule on the AACOMAS side, and it is the kind that costs people a cycle.

Both cap at ten. AMCAS: "You may have up to 10 letters associated with your AMCAS application." AACOMAS: "You can enter information for a maximum of 10 evaluations," and "If you want to submit more, send those additional evaluations directly to your programs." On AACOMAS, "a committee letter only counts as one evaluation and the individuals who contributed to the letter may not be used as additional evaluators."

Neither requires letters before you submit. AMCAS: "Letters are not required to submit your application, or have your application verified by the AMCAS program." AACOMAS: "You can submit your application before your transcripts and evaluations are received."

After submission they part ways. AMCAS: "you can only make additions of up to 10 letters, and you must notify the AMCAS program if you have a letter you wish to no longer be sent to medical schools; you cannot delete letters of evaluation from your application." AACOMAS: "You can edit and delete evaluations with Requested or Accepted statuses."

None of the pages fetched for this article say whether one person may use both. What both do say is that programs can be added after submission. AACOMAS: "You can select additional programs to apply to." AMCAS: "You can send your application to additional medical schools if their application deadlines have not passed." AMCAS adds that the list cannot shrink: "Once you have submitted your application to the AMCAS program, you can't remove or substitute schools on your designation list under any circumstances."

So these are two separate systems with separate fees, separate waivers, and separate school lists. Whether both belong in one person's plan is a question for your prehealth advisor, not for a newsletter.

Alex