- The Headline Number: 88% in 2025
- What the 88% Does and Does Not Tell You
- Pass Rate vs. 75% Passing Score
- Why a 25-Sitting Sample Demands Caution
- What About 2026?
- Who Actually Sits the Exam
- Domain-by-Domain Readiness
- A CMI-Specific Preparation Sequence
- Exam-Day Logistics That Protect Your Score
- What a Miss Costs You
- Frequently Asked Questions
- ACAC's 2025 Exam Pass Ratio reports 88% for CMI: 22 passes from 25 examinations.
- That figure includes retakes and state-licensing-only sittings, so it is not a first-attempt pass rate.
- No 2026 CMI pass rate has been verified; treat any claimed 2026 figure with suspicion.
- The pass rate is separate from the 75% passing score on a 100-question, three-hour exam.
The Headline Number: 88% in 2025
If you are researching the Council-certified Microbial Investigator credential, the most useful single data point comes straight from the issuer. The American Council for Accredited Certification (ACAC) publishes an annual Exam Pass Ratio report, and its 2025 edition lists the CMI at 88%, representing 22 passes out of 25 CMI examinations.
That is a primary-source figure, which makes it more trustworthy than the pass-rate claims scattered across third-party prep sites. Some of those sites assert that ACAC does not publish CMI pass rates at all. That claim is wrong: the report exists, it breaks results out by credential, and it is available on ACAC's website. If you want the broader picture of how demanding the exam is beyond a single percentage, our guide on how hard the CMI exam is puts the number in context.
This article explains what the 88% actually measures, what it cannot tell you, and how to turn it into a realistic preparation plan built around the six official exam domains.
What the 88% Does and Does Not Tell You
What it measures
The figure is a ratio of passing results to total CMI examinations recorded in the reporting year. In 2025 that was 22 of 25. It is an aggregate across everyone who sat the exam, regardless of their background, preparation route, or how many times they had tried before.
What it does not measure
ACAC's report carries limitations that matter for how you read it:
- It includes retakes. A candidate who failed once and passed on a second sitting contributes both a failure and a pass. The report does not disclose how many CMI sittings were retakes.
- It includes state-licensing-only examinations. Some people sit the exam solely to satisfy a state licensing requirement. Passing it for that purpose does not itself award CMI certification, and the report does not say how many CMI sittings fall into this category.
- It is not a first-attempt rate. You cannot read 88% as "88% of first-time candidates pass."
- It does not predict your result. It describes a population in a past year, not your odds.
Pass Rate vs. 75% Passing Score
Candidates frequently confuse two different numbers, so it is worth separating them clearly.
| Concept | What it is | CMI value |
|---|---|---|
| Pass rate | Share of exam sittings that ended in a pass, reported by ACAC for a given year | 88% (22 of 25) in 2025 |
| Passing score | The cut score you must reach on your own exam, set with the Modified Angoff method | 75% |
| Exam format | Computer-delivered, closed-book, multiple choice, delivered through Kryterion | 100 questions, 3 hours |
The passing score is a standard applied to you individually. The pass rate is an outcome statistic about a group. A high pass rate does not lower the 75% bar, and the bar does not tell you how many people clear it. For a detailed look at how the cut score works, see our breakdown of the CMI passing score.
The Modified Angoff method means a panel of subject-matter experts judged how a minimally competent candidate would perform on each item, and that judgment produced the 75% threshold. It is a criterion-referenced standard: you are not graded against other test-takers, so a strong cohort does not push your cut score upward.
Why a 25-Sitting Sample Demands Caution
Statistically, 25 is a small number. Three failures out of 25 produced the 88%. If just one more candidate had failed, the figure would have fallen noticeably; if one of those three had passed, it would have risen. A pass rate built on this few observations can swing from year to year without any real change in exam difficulty or candidate quality.
The same caution applies to the certification population. ACAC's accredited certification activity report, covering the period through December 31, 2025, lists 25 CMI applicants, 59 recertifications, and 166 current certifications. These are modest numbers. The CMI is a specialized credential with a small community, which is exactly why the annual pass ratio should be treated as a rough indicator rather than a precise measurement.
What About 2026?
As of the most recent verification, no 2026 CMI pass rate has been published or confirmed. ACAC's report is annual, so the 2025 figure remains the latest issuer-backed data point. No separately labeled 2026 exam version has been verified either; the current formal chart of exam domains was approved February 21, 2024.
Be skeptical of any site that presents a specific 2026 pass percentage for the CMI, or that markets a "2026/2027" guide as though it reflects a new exam version. Unless it cites an ACAC document, it is guessing. When you need dates and scheduling details rather than statistics, our CMI exam dates guide covers testing windows and the application timeline.
Who Actually Sits the Exam
Understanding the candidate pool helps you interpret the pass rate. CMI candidates are not casual test-takers; they must clear eligibility screening before they ever see a question. The pathways are:
- A related two-year postsecondary degree, or an equivalent 15 qualifying college credits, plus at least one year of documented microbial sampling experience; or
- A high school diploma or GED plus two years of consulting experience in microbial sampling.
Related fields include microbiology, engineering, science, architecture, and industrial hygiene. Candidates must demonstrate that they can design, conduct, and interpret microbial sampling regimens, and the application requires four project sheets, academic evidence where applicable, and experience verification. ACAC's eligibility FAQ adds that at least one full year of actual field experience is required regardless of college credits.
This screening is a likely contributor to the strong pass ratio: the people reaching the exam room already have hands-on sampling experience. Full detail on qualifying is in our CMI requirements guide.
Domain-by-Domain Readiness
ACAC's formal chart organizes the exam into six domains. No official percentage weights are published, so there is no verified way to say which domain carries the most questions. Some third-party prep sites publish approximate allocations; those describe their own practice materials, not the real exam. Plan for balanced coverage, and see the complete guide to all six CMI exam domains for subdomain detail.
Domain 1: Scientific knowledge of biological agents
The foundation for everything else. You need to recognize the organisms and biological contaminants encountered in indoor environments and understand their characteristics.
- Know the groups of biological agents relevant to indoor environmental investigations
- Understand growth requirements and conditions that favor amplification
- Connect biological behavior to what sampling can and cannot detect
Domain 2: Potential health effects and risks associated with exposure
Linking biological agents to human outcomes, with appropriate caution about what evidence supports.
- Understand exposure routes and the range of potential health effects
- Recognize the limits of what a sampling result can say about health
- Distinguish hazard from risk in your reasoning
Domain 3: Principles of Microbial Investigation
How an investigation is structured, from initial assessment to conclusions.
- Build an investigation around a defensible hypothesis and scope
- Interpret observations and building conditions alongside data
- Document findings in a way that supports your conclusions
Domain 4: Principles of Microbial Sampling
The area most directly tied to the experience requirement. Eligibility itself rests on your ability to design, conduct, and interpret sampling regimens.
- Select sampling methods that match the question being asked
- Understand controls, comparison samples, and sources of error
- Interpret results rather than merely reporting them
Domain 5: Principles of Microbial Remediation
What happens after the investigation, including how remediation is specified and how success is judged.
- Know the principles reflected in the IICRC water-damage and mold-remediation standards on the reference list
- Understand containment concepts and verification of results
- Recognize where an investigator's role ends and a remediator's begins
Domain 6: Health & Safety
Easy to underestimate, and a known trap: ACAC's shorter five-topic handbook summary omits this domain, but the formal approved chart includes it. The formal chart controls.
- Study respiratory protection using the OSHA and NIOSH references on the bibliography
- Understand respirator selection logic and compliance expectations
- Apply safety thinking to field sampling and remediation settings
A CMI-Specific Preparation Sequence
Because the pass rate is a population statistic and not a promise, the useful move is to convert it into a sequence that fits how the six domains build on each other. The schedule below is one reasonable ordering, not an official requirement. It assumes you already meet the field-experience prerequisites.
Domains 1 and 2: Biology and health
- Establish the scientific vocabulary that everything later depends on
- Begin working through the AIHA field guide on biological contaminants
Domains 3 and 4: Investigation and sampling
- Review ACGIH Bioaerosols: Assessment and Control for sampling and interpretation
- Practice reasoning from a scenario to a sampling plan to an interpretation
Domain 5: Remediation
- Read the relevant IICRC S500 water-damage and S520 mold-remediation material
- Confirm which edition of each standard you are studying (see below)
Domain 6 plus full-length review
- Work through the OSHA respiratory protection compliance guide and NIOSH Respirator Selection Logic
- Finish with timed, 100-question mixed practice under closed-book conditions
For a fuller approach to building your plan, see the CMI study guide, and for a quick refresher on core facts, the CMI cheat sheet.
Know your reference editions
The handbook lists specific bibliographic references, including explicit edition alternatives. These are listings, not a statement that the exam was revised to a particular edition, and the full paid texts are not provided by ACAC.
- ACGIH, Bioaerosols: Assessment and Control, first edition (1999) or second edition (2024)
- AIHA, Field Guide for the Determination of Biological Contaminants, second edition (2005)
- ANSI/IICRC S500-2021, Standard for Professional Water Damage Restoration, fifth edition
- ANSI/IICRC S520-2015 and IICRC R520-2015 (third editions) or ANSI/IICRC S520-2024, fourth edition
- OSHA, Small Entity Compliance Guide for the Respiratory Protection Standard (2011)
- NIOSH, Respirator Selection Logic (2004)
Exam-Day Logistics That Protect Your Score
Avoidable logistics problems cost candidates more than a missed fact ever will. The verified format is a computer-delivered, closed-book written exam through Kryterion: 100 multiple-choice questions with at least four answer options each, completed in three hours. The handbook describes a fixed question set with randomized question and answer order, immediate electronic scoring, and an emailed result. Adaptive testing is not described, and the scored versus unscored split is not published. No separate practical assessment is described.
- Testing-center candidates need two government-issued IDs, including one photo ID.
- Online candidates need their own computer, an approved webcam, and a private location, with at least 2 Mbps upload and download speeds. Phones and tablets are excluded.
- Arrival time is documented inconsistently: ACAC's exams page says 15 minutes early, while the handbook says 30. Plan for the longer window.
The application process also carries unresolved discrepancies between ACAC's current application page and the handbook, covering timeframe, notarization, and how often the board meets. Confirm current requirements with ACAC directly before relying on any single source. Our overview of what CMI certification involves gives the broader orientation.
What a Miss Costs You
A strong pass ratio is reassuring, but understanding the financial side of a retake keeps the stakes in perspective. The initial two-year term costs a total of $500: a $100 examination fee plus a $400 certification fee. The $400 certification fee includes a $100 nonrefundable processing fee, which is not an additional charge. A retake costs $100, and renewal is $400. No separate member or nonmember fee schedule is published.
| Item | Fee (USD) |
|---|---|
| Examination | $100 |
| Certification (initial two-year term) | $400 |
| Initial total | $500 |
| Retake | $100 |
| Renewal | $400 |
A retake is relatively inexpensive in direct fees, but the larger cost is time, plus the delay in holding the credential. For a complete breakdown, read our CMI certification cost guide. If you are weighing whether the investment pays off, the ROI analysis and the salary guide discuss it honestly; note that no reliable salary survey specific to ACAC CMI holders, and no verified causal earnings premium, currently exists.
Once certified, the credential runs for two years. Renewal involves 40 recertification credits (RCs), with the detailed procedure specifying 10 for continued field activity and 30 for professional development, plus attestation and retained documentation in case of audit. ACAC's own pages describe the professional-development portion differently in places, so verify the current requirement at renewal time.
Ready to test where you stand against the six domains? Try the CMI practice tests to find your weak spots before exam day, and use the timed mixed sets from the main practice site in your final week.
Frequently Asked Questions
ACAC's 2025 Exam Pass Ratio reports 88% for the Council-certified Microbial Investigator exam, with 22 passes from 25 examinations. This is the most recent issuer-published figure; no 2026 pass rate has been verified.
No. The report includes retakes and state-licensing-only examinations and does not say how many CMI sittings fall into either group. It cannot be read as a first-attempt rate or used to predict your individual result.
The pass rate is the share of sittings that ended in a pass. The passing score is the 75% you must reach on your own 100-question exam, set using the Modified Angoff method. One describes a group's outcomes; the other is your personal threshold.
The 2025 figure rests on only 25 examinations, so a single additional pass or failure shifts the percentage noticeably. Year-to-year changes in a sample this small often reflect noise rather than a real change in difficulty.
ACAC's formal chart lists six domains but publishes no official percentage weights, so no highest-weighted domain can be established. Any percentages you see on prep sites describe those sites' practice materials, not the actual exam.