CMI Certification

What the Council-certified Microbial Investigator Credential Is

The Council-certified Microbial Investigator credential is awarded by the American Council for Accredited Certification (ACAC) through its CMI Certification Board. The program is accredited by the Council for Engineering and Scientific Specialty Boards (CESB). The credential targets professionals who design, conduct and interpret microbial sampling regimens in the built environment, typically in the context of mold, moisture and indoor air quality investigations.

If you are new to the terminology, our explainers on what CMI certification is and what CMI stands for cover the basics. This article goes deeper into the mechanics: who qualifies, what the exam looks like, how the six domains break down, and where ACAC's own published materials disagree with each other.

One related credential worth distinguishing is the Council-certified Microbial Consultant (CMC), which ACAC examines under a shared domain chart. CMC has its own advanced education and experience pathways, and those do not transfer to CMI. If you are weighing the two, check each pathway's requirements separately rather than assuming they mirror each other.

Eligibility Pathways and Project Sheets

ACAC publishes two routes to CMI eligibility. Both hinge on documented microbial sampling experience, not just coursework.

Related fields named by ACAC include microbiology, engineering, science, architecture and industrial hygiene. ACAC's eligibility FAQ clarifies an important point: even with qualifying college credits, you need at least one full year of actual field experience. Credits cannot substitute for fieldwork.

Candidates must demonstrate the ability to design, conduct and interpret microbial sampling regimens. The application requires four project sheets, applicable academic evidence and experience verification. No mandatory preparation course or minimum training-hour requirement is published. For a fuller walk-through, see our guide to CMI requirements, eligibility and prerequisites.

Exam Mechanics: Format, Delivery and Scoring

Format at a glance

• Test provider: Kryterion, Inc.
• Questions: 100 multiple-choice items, each with at least four answer options
• Time limit: three hours, computer-delivered
• Reference materials: closed book
• Passing score: 75%, established using the Modified Angoff method
• Practical component: none described; the written exam is the assessment

The Modified Angoff method means the cut score reflects expert judgment about how a minimally qualified candidate would perform on each item, rather than a fixed curve against other test takers. ACAC does not publish how many of the 100 items are scored versus unscored, so do not assume every question counts or that any given question is a pretest item. Our passing score breakdown covers what the 75% threshold means in practice.

Delivery and day-of logistics

The exam can be taken at a proctored testing center or by online video proctoring. 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. Whether a calculator is permitted is not verified in the public materials, so confirm with ACAC or Kryterion before exam day rather than assuming.

• Testing center: bring two government-issued IDs, including one with a photo.
• Online: you supply a computer, an approved webcam and a private location. ACAC specifies at least 2 Mbps upload and download speed, and phones and tablets are excluded.
• Arrival: ACAC's exam page says to arrive 15 minutes early, while the candidate handbook says 30. Plan for the longer window to be safe.

For scheduling specifics, see CMI exam dates, testing windows and deadlines. If you want a sense of the challenge before committing, read how hard the CMI exam is.

The Six Official Exam Domains

ACAC's formal exam-domain chart, approved February 21, 2024, is the controlling document. It lists six exam domains, with numbered subdomain columns beneath them. Those columns numbered 1 through 7 are subdomains, not seven additional domains. Importantly, ACAC publishes no percentage weights for the domains, so no single domain can be identified as the heaviest. Treat all six as testable and be suspicious of any third-party resource that presents its own percentage split as official.

The candidate handbook's shorter summary lists only five topics and omits the separate Health & Safety domain that appears in the formal chart. Where they differ, the formal chart controls. Our complete guide to all six CMI content areas expands on each.

Because Health & Safety is missing from the handbook's shorter summary, some candidates under-prepare for it. The official reference list includes OSHA and NIOSH respiratory protection documents, which signals that this domain deserves deliberate study time.

Fees, Application Timeline and Unresolved Issuer Discrepancies

The $100 processing fee is part of the $400 certification fee, not an extra charge. ACAC does not publish a separate member and nonmember fee schedule. Our full CMI cost breakdown walks through budgeting, including preparation materials.

Where ACAC's own pages disagree

Candidates should know that ACAC's published materials contain conflicts that remain unresolved as of the last review. Verify these directly with ACAC before you submit.

• Application window: The current application page describes six months including the examination, with unanimous board approval and a board that meets every four to six weeks. The handbook instead describes 90 days, notarized forms or employer affidavits, and board meetings about every four weeks.
• Early arrival: 15 minutes on the exam page versus 30 minutes in the handbook.
• Handbook typos: Within the CMI section, the body-of-knowledge introduction mistakenly names CMC and a designation-use heading says CIE. The explicit CMI examination section and the jointly titled official chart establish that the CMI scope applies.

The Reference Library and Edition Choices

The CMI handbook lists specific references and, in several cases, explicitly published edition alternatives. These bibliographic listings do not establish an exam revision, and they do not mean any particular text is the sole source of questions.

The domain mapping in the right-hand column is a study aid, not an official crosswalk; ACAC does not publish one. The handbook also includes selected study-guide passages, but it warns that these pages are illustrative and that candidates need comprehensive knowledge of the reference texts. Note too that although the OSHA guide appears in the CMI bibliography, the CMI study-guide section does not supply a page or section subset for it. Read the whole document rather than hunting for a "tested excerpt."

Reading the 2025 Pass Data Honestly

ACAC's 2025 Exam Pass Ratio reports an 88% pass rate for CMI, representing 22 passes from 25 examinations. That is a real, issuer-published figure, and it contradicts claims on some third-party sites that ACAC does not publish CMI pass rates. But it should be read with care:

• The sample is small, just 25 examinations, so a single result moves the percentage noticeably.
• The report includes retakes and state-licensing-only examinations, and it does not disclose how many CMI sittings fall into either category.
• It does not establish first-attempt success and cannot predict your individual result.
• No 2026 pass rate has been verified.

Do not confuse the 88% observed pass rate with the 75% passing score. One describes how a group performed in a year; the other is the score you must reach on your own exam. For deeper context, see our CMI pass rate analysis.

ACAC's Accredited Certification Activity report as of December 31, 2025 lists 25 CMI applicants, 59 recertifications and 166 current certifications. These are issuer counts, not search-demand estimates, and they show that CMI is a small, specialized credential rather than a mass-market one.

Sequencing Your Preparation Around the Domains

Rather than a generic study calendar, build your schedule around how the domains depend on each other. Foundational science feeds investigation logic, which feeds sampling design, which feeds remediation and safety decisions. A sequence like the one below respects that dependency chain. Adjust the pace to your experience; a working sampler may compress the early weeks, while someone newer to field work may need more time on Domain 4.

Choosing preparation resources

Several third-party sites offer CMI-specific practice content, but quality and alignment vary, and none of it is an official ACAC product. When evaluating a resource, ask whether it covers all six official domains, whether it cites the actual reference editions, and whether its explanations teach reasoning rather than just answers. Be cautious of generic previews that do not mention microbial sampling at all. You can start with free questions on our CMI practice test site and use the results to decide where to focus your reading. ACAC also maintains a directory of accredited training providers, but confirm that any course aligns with the CMI exam specifically; a provider's own licensing exam or course length is not the CMI written exam.

Renewal, Career Value and Salary Caveats

Keeping the credential

CMI is valid for two years. ACAC's detailed recertification procedure specifies 40 recertification credits (RCs): 10 for continued field activity and 30 for professional development during the term. You attest to the credits and must retain documentation in case of audit, and a current photo is requested. Renewal costs $400.

Here too the sources differ: the handbook uses general 40-RC wording, and the program page refers to 20 professional-development hours per year. The detailed procedure is the most specific, so track credits against it and confirm with ACAC if your situation is borderline.

Who uses the credential, and what it may be worth

CMI is relevant to indoor environmental consultants, industrial hygiene practitioners, restoration and remediation professionals, building science and architecture-adjacent roles, and engineers who handle moisture and air quality assessments. For a sense of the work, browse our overview of CMI jobs and the CMI training landscape.

On compensation, be skeptical of precise figures. No reliable salary survey specific to ACAC CMI holders has been verified, and there is no established causal earnings premium from holding the credential. Pay in this field depends heavily on region, employer type, licensing environment and years of field experience. A sensible way to think about return is qualitative: the credential documents your sampling competence to clients, employers and in some cases regulators, and at $500 for the first term it is a modest investment relative to many professional certifications. Our salary guide and ROI analysis separate occupational pay evidence from claims about certification value.

Frequently Asked Questions

CMI rewards candidates who can connect biology, investigation logic, sampling design, remediation principles and safety practice into one coherent line of reasoning. Verify the current rules with ACAC, work through the official references edition by edition, and test yourself against realistic timed questions on our practice test platform before you sit for the exam.