- The Number: 75% on a 120-Question Exam
- What 75% Means in Practice
- How the Cut Score Was Set
- Passing Score vs. Pass Rate
- Spreading Your Points Across Six Domains
- Exam Format, Delivery and Score Reporting
- The Score Is Only One Gate
- If You Miss the Mark: Retake Mechanics
- A Score-Targeting Plan Built Around the Domains
- Frequently Asked Questions
- The ACAC Council-certified Microbial Consultant exam requires a 75% passing score on 120 multiple-choice questions.
- The cut score was set using a Modified Angoff method, not by curving against other candidates.
- ACAC's 2025 pass ratio was 94% (16 of 17 attempts), which is a different measure from the 75% score.
- The exam is closed book, three hours, computer-delivered, and results are shown electronically right away.
The Number: 75% on a 120-Question Exam
The passing standard for the Council-certified Microbial Consultant (CMC) examination, administered through the American Council for Accredited Certification (ACAC) and its CMC Certification Board, is a 75% passing score. The exam consists of 120 multiple-choice questions, each with at least four answer options, delivered on a computer over three hours in a closed-book setting. The program is accredited by the Council for Engineering and Scientific Specialty Boards (CESB), and the exam is delivered through Kryterion, Inc.
That is the whole headline: three-quarters of the scored content, correctly answered, inside a 180-minute window. Everything else in this article is about what that number really means, how to plan around it, and which common misreadings can cost you preparation time. If you want the broader picture of how difficult candidates find the test, see our complete CMC difficulty guide.
What 75% Means in Practice
On a 120-question exam, 75% would translate to 90 correct answers if every question were scored. That arithmetic comes with an important caveat: ACAC has not published whether all 120 items are scored or whether some are unscored pretest items. Because the scored/unscored split is not public, treat 90 as a planning reference rather than a guaranteed raw cutoff.
The practical consequence is straightforward. You can miss roughly one question in four and still be in passing territory, but you cannot know in advance which items count. The safest approach is to treat every question as scored and never "write off" a question because it looks unusual.
Why a Planning Buffer Matters
Because you cannot see which items are scored, aiming for exactly the minimum leaves no margin. Candidates who consistently score a comfortable distance above 75% on honest, closed-book practice have a far better position than those who hover at the line. Our CMC practice test is designed so you can measure where you stand against the 75% benchmark under timed conditions.
How the Cut Score Was Set
The 75% standard was established using a Modified Angoff procedure. In an Angoff-style study, subject-matter experts review each exam question and estimate the probability that a minimally competent candidate would answer it correctly. Those judgments are aggregated into a recommended passing standard. The "modified" variant typically adds discussion rounds and reference data to refine the estimates.
Two implications follow for candidates:
- It is criterion-referenced. You are measured against a defined competence standard, not against the other people who tested the same week. A strong cohort does not raise the bar, and a weak one does not lower it.
- It reflects "minimally competent," not "expert." The standard is built around what a just-qualified consultant should know, which is why the questions emphasize applied judgment in sampling and interpretation rather than obscure trivia.
Passing Score vs. Pass Rate
These two figures get confused constantly, and some third-party sites have even claimed ACAC publishes no CMC pass-rate data. It does. ACAC's 2025 Exam Pass Ratio reports a 94% pass rate, with 16 passes from 17 attempts.
| Measure | What It Is | Value for the ACAC CMC |
|---|---|---|
| Passing score | The percentage of the exam you must answer correctly | 75%, set by Modified Angoff |
| Pass rate | The share of exam attempts that resulted in a pass | 94% in 2025 (16 of 17 attempts) |
| Sample caveat | Who is counted in the attempts | Includes retakes and state-licensing-only candidates; not first-attempt-only |
| 2026 rate | Current-year result | Not verified at the time of writing |
Read the 94% figure carefully. It is based on a very small number of attempts, it blends first-time and repeat candidates, and it includes candidates sitting for state-licensing purposes only. It is encouraging, but it is not a promise about your odds, and it says nothing about how long candidates prepared. For a deeper look at what the data does and does not support, read our CMC pass rate analysis.
Spreading Your Points Across Six Domains
ACAC's formal exam-domain chart (approved February 21, 2024) lists six domains. No percentage weights are published, so you cannot responsibly claim that one domain carries the most questions. Some third-party resources divide their practice material into roughly equal categories, but those are publisher choices, not official weights. With a 75% bar and unknown weighting, the sound strategy is balanced competence with no domain left weak.
Domain 1: Scientific knowledge of biological agents
The foundation: what organisms you are dealing with and how they behave in built environments.
- Fungal, bacterial and other biological agents relevant to indoor environments
- Growth requirements, moisture relationships and amplification conditions
- Biological contaminants as described in the AIHA field guide referenced by ACAC
Domain 2: Potential health effects and risks associated with exposure
Linking exposure to outcomes without overstating causation.
- Exposure pathways and susceptible populations
- Appropriate framing of risk and the limits of what sampling data can say about health
- Microbial risk analysis concepts
Domain 3: Principles of Microbial Investigation
How a consultant structures an investigation from complaint to conclusion.
- Building-science reasoning: moisture sources, airflow and building envelope
- Hypothesis development, visual assessment and documentation
- Deciding when sampling is warranted at all
Domain 4: Principles of Microbial Sampling
The heart of the credential, and the area ACAC's experience requirement targets directly: designing, conducting and interpreting sampling regimens.
- Air, surface and bulk sampling methods and when each is appropriate
- Sampling design, controls, calibration and chain of custody
- Interpreting results and recognizing the limitations of the data
- Bioaerosol assessment and control concepts from the ACGIH reference
Domain 5: Principles of Microbial Remediation
What happens after the investigation, including how to verify that work was effective.
- Remediation principles and containment concepts aligned with ANSI/IICRC S520
- Water-damage context drawn from ANSI/IICRC S500
- Remediation documentation and post-remediation verification
Domain 6: Health & Safety
Easy to under-study because it can feel like common knowledge. It is a standalone formal domain, so do not skip it.
- Respiratory protection, as covered in the OSHA Small Entity Compliance Guide for the Respiratory Protection Standard
- Respirator selection logic from the NIOSH reference
- Protecting workers and occupants during investigation and remediation
A full breakdown of the official objectives is in our guide to all six CMC content areas. One detail worth knowing: ACAC's handbook describes a shorter five-topic body of knowledge that omits Health & Safety as its own topic, while the formal domain chart includes it. When sources disagree, prepare for the larger scope.
Exam Format, Delivery and Score Reporting
Understanding the mechanics helps you protect your score from avoidable problems.
- Delivery: Testing-center or online video proctoring, scheduled through ACAC.
- Question handling: The handbook describes the same question set for everyone, with randomized question and answer order. Adaptive testing is not described.
- Results: Immediate electronic scores, followed by emailed results.
- Arrival: The current ACAC Examinations page says to arrive 15 minutes early; the handbook says 30. Because the sources conflict, plan for the longer window.
- Identification: Testing-center candidates need two government-issued IDs, one of which must be a photo ID.
- Online requirements: A computer, an approved webcam, a private location, and at least 2 Mbps upload and download speed. Phones and tablets are excluded.
- Calculator policy: Not verified. Confirm with ACAC before exam day rather than assuming.
Three hours for 120 questions averages out to 90 seconds per question. That is generous for recall items and tighter for scenario-based questions that require you to interpret sampling data or reason through a remediation sequence. Practice at this pace; scheduling and logistics are covered further in our CMC exam dates and scheduling guide.
The Score Is Only One Gate
Passing the exam does not by itself make you a Council-certified Microbial Consultant. Certification also depends on your application being approved, and a result on a licensing-only exam does not confer the credential.
Key Takeaway
Eligibility is the first hurdle, and it is documentation-heavy. ACAC accepts a related four-year degree (or 30 qualifying credits) with four years of documented microbial sampling; a related two-year degree (or 15 qualifying credits) with six years; or a high school diploma/GED with eight years of consulting experience in microbial sampling. Four project sheets, transcripts and experience verification are required, and the board must approve unanimously.
Qualifying fields include microbiology, engineering, science, architecture and industrial hygiene, while social sciences are excluded from qualifying coursework. The full rundown is in our CMC requirements guide.
One issuer inconsistency deserves a warning. ACAC's current application page describes a process of about six months including the exam, with the board meeting every four to six weeks, while the handbook describes 90 days and notarized forms with employer affidavits. This conflict is unresolved in the sources, so confirm current procedures directly with ACAC before building a timeline.
If You Miss the Mark: Retake Mechanics
The published fee structure is simple. The examination fee is $100 and the certification fee is $400 (including $100 nonrefundable processing), for a total of $500 covering the initial two-year term. A retake costs $100, and renewal is $400. No separate member and non-member schedule is published. Full pricing context is in our CMC certification cost breakdown.
A failed attempt is financially modest compared with the rest of the certification path, but it still costs time and momentum. The better use of that knowledge is to treat your first attempt as the real one and prepare accordingly.
A Score-Targeting Plan Built Around the Domains
Because no domain weights are published and the exam assumes comprehensive knowledge of the listed references, sequence your preparation by dependency rather than by guesswork. A plan like this one works well for candidates who already have field experience:
Biology and Health (Domains 1 and 2)
- Build vocabulary and growth-condition fundamentals first, since later domains lean on them
- Use the AIHA biological contaminants field guide as your anchor reference
Investigation and Sampling (Domains 3 and 4)
- Spend the most time here if sampling interpretation is not your daily work
- Work through sampling design, controls and data limitations using the ACGIH bioaerosol reference
Remediation and Safety (Domains 5 and 6)
- Study the S500 and S520 editions your handbook lists
- Review OSHA respiratory protection and NIOSH selection logic so Health & Safety is not your weak link
Timed Full-Length Practice
- Run closed-book, three-hour simulations and review every miss by domain
- Target a margin comfortably above 75% before booking
Two reference cautions. First, the handbook allows alternate editions for some titles (for example, the ACGIH bioaerosols book in its 1999 or 2024 edition, and S520 in its 2015 or 2024 edition); this does not establish an exam revision date, so study the editions ACAC lists. Second, the handbook explicitly warns that its selected study-guide sections and page references are examples, not an exhaustive prep list. Do not study only the highlighted pages. For a full study framework, see our CMC study guide, and keep our one-page cheat sheet handy for final review.
Using Practice Questions Honestly
Third-party question banks vary in quality and alignment. Some publish mock exams with their own settings (such as shorter lengths or different pass marks), and those settings should never replace the official 120-question, three-hour, 75% standard. Use practice material to find gaps by domain, not to predict your exact score. You can start with our free CMC practice questions and track results domain by domain.
Frequently Asked Questions
The passing score is 75%, set using a Modified Angoff method. The exam has 120 multiple-choice questions, runs three hours, and is closed book. The split between scored and unscored questions is not published.
No. The 75% standard is criterion-referenced, meaning it reflects a defined competence level rather than how other candidates performed. Your result depends on your own answers, not on the cohort you test with.
No. The 75% is the score you must reach on the exam. The 94% figure (16 passes from 17 attempts in 2025) is the share of attempts that passed. It includes retakes and state-licensing-only candidates, and no 2026 rate was verified.
The handbook describes immediate electronic scoring on completion, followed by emailed results. Passing the exam alone does not confer certification, because your application must also be approved by the board.
That cannot be established. ACAC publishes six domains without percentage weights. Prepare across all six, including Health & Safety, rather than concentrating on a single area.
A retake costs $100. The initial total of $500 covers the exam fee ($100) and certification fee ($400) for the first two-year term, and renewal is $400. For what certification may mean for your income, see our salary guide and ROI analysis.