The Certified Mold Inspector (CMI) credential from the American Council for Accredited Certification (ACAC) is for people who inspect buildings for mold and moisture problems. This page gives you free practice sets by topic, worked answers to sample questions, the main exam facts from the ACAC handbook, and a study plan. The exam has 100 questions, a 3-hour limit and a 75% passing score.
The CMI has 100 questions and takes about 3 hours[1] (American Council for Accredited Certification, verified Oct 25, 2026).
Numbers in brackets link to the official sources listed under Sources & last verified. Dates that have passed are removed automatically.
| Item | Detail | Source · Verified |
|---|---|---|
| Number of questions | 100 questions, closed-book[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Time limit | 3 hours[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Passing score | 75% (Modified Angoff)[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Retake fee | $100 per re-examination[2] | American Council for Accredited Certification · Oct 25, 2026 |
| Retake policy | Retest at your convenience by calling ACAC[2] | American Council for Accredited Certification · Oct 25, 2026 |
| Validity | 2 years from date of issue[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Renewal | 40 Re-certification Credits every 2 years[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Delivery | Computer-based, at a testing facility or by online proctoring[2] | American Council for Accredited Certification · Oct 25, 2026 |
| Eligibility | 2-year degree + 1 year, or no degree + 2 years microbial sampling experience[1] | American Council for Accredited Certification · Oct 25, 2026 |
| Score release | Immediately after grading[2] | American Council for Accredited Certification · Oct 25, 2026 |
| Registration deadline | Up to 90 days from application to complete it[1] | American Council for Accredited Certification · Oct 25, 2026 |
According to American Council for Accredited Certification, “A score of 75% must be achieved to pass this examination.”[1]
The CMI exam checks whether a candidate can carry out mold inspection and assessment work to the standard ACAC sets for this certification. It is computer-based and taken in the presence of a proctor, either at a testing facility or through online proctoring.
The exam has 100 questions, is closed-book, and has a 3-hour time limit. ACAC sets the passing mark at 75% using the Modified Angoff method, where the cut score is based on what a minimally qualified candidate should know. Exams are graded electronically, and you see your score right away.
To be eligible you need either a 2-year post-secondary degree (or its equivalent) plus 1 year of microbial sampling experience, or no degree and 2 years of that experience. Once you apply, you have up to 90 days to finish the application process.
If you fail, you can retest whenever you are ready by calling the ACAC office. Each re-examination costs $100. The certification is current for 2 years from the date of issue, and to renew it you need 40 Re-certification Credits every 2 years.
ACAC certification is not the same as a state license. Some states regulate mold inspection separately, and their rules differ, so check with your state as well. Before you apply, confirm the current details in the official CMI handbook at acac.org.
Prepare for the CMI - Certified Mold Inspector exam with our free practice test modules. Each quiz covers key topics to help you pass on your first try.
These are practice questions written for this site, not questions from the real exam. Each explanation shows why the right answer is right and why the others are wrong.
Question: Which type of wall assembly is most prone to interstitial condensation and mold growth in a hot, humid climate?
Answer: A. Assembly with a vapor retarder on the interior (warm-in-winter) side, which is the wrong side in a cooling-dominant climate
Explanation:
A is correct. In a hot, humid, cooling-dominant climate, water vapor usually moves from the warm, moist outdoors toward the cool, air-conditioned interior. A vapor retarder on the interior side is the standard cold-climate detail, but here it sits on the cool side of the wall. Moisture moving inward builds up against it or condenses on cool sheathing, and the wall cannot dry to the inside. That is where mold grows.
B is wrong: exterior rigid foam keeps the sheathing warmer and is a common way to lower condensation risk. C is wrong: a rainscreen gap lets water drain and helps the back of the cladding dry. D is wrong: open-joint cladding over a weather-resistant barrier depends on drainage and airflow behind the cladding, which also helps drying.
Rule: put vapor control on the warm, moist side and let the wall dry toward the other side.
Question: Which method is used to measure carbon monoxide levels indoors?
Answer: B. Carbon monoxide detector
Explanation:
B is correct. Carbon monoxide is colorless and odorless, so you can only detect it with a sensor built for that gas, such as a carbon monoxide detector or meter. During an inspection, any fuel-burning appliance is a possible source.
A is wrong: an infrared thermometer measures surface temperature. That helps you find cold spots where condensation may form, but it cannot detect gases. C is wrong: a UV light can show some stains and residues that glow under it, but it does not measure the concentration of anything in the air. D is wrong: a humidity gauge (hygrometer) measures relative humidity. That matters a lot for mold, but it tells you nothing about carbon monoxide.
Rule: pick the instrument by what it actually measures, and do not read one tool's result as evidence about something else.
Question: What role does client communication play in mold inspection reporting?
Answer: C. It ensures client understanding of the report
Explanation:
C is correct. A report only helps if the client understands it. Talking the client through it makes sure they see what was found, how serious it is, what was and was not inspected, and what to do next, so they can make an informed decision about remediation.
A is wrong: clear communication often takes more time, not less, and saving time is not the point. B is wrong: talking with the client does not replace the written report, which is the permanent record of the inspection. D is wrong: clear communication does help with liability, for example by setting out the scope and its limits, but that is a side benefit and not the only reason to do it.
Rule: explain findings, limits and recommendations in plain language, and write down what you discussed with the client.
Start by reading the official CMI handbook from ACAC so you know the eligibility rules, the application window and what the exam covers. Then take the Start Practice Test set to get a baseline and see which topics feel weakest.
Spend most of your time on those weak topics. If building science is the gap, work through Moisture Intrusion & Building Science and Building Materials & Construction Systems. For fieldwork, use Mold Identification & Sampling Techniques and Post-Remediation Clearance Testing. For the written side, use Mold Inspection Report Writing.
After each set, read every explanation, including the ones for questions you got right, and write down the general rule in a sentence. Keep these notes short so you can review them the week before the exam.
As test day gets close, practice the way the real exam works: closed-book and timed, aiming for 100 questions in 3 hours. Go back over any topic where you still miss questions, and check your application details with ACAC so nothing is left unfinished.
The CMI exam has 100 questions, and you have 3 hours to finish. It is closed-book, so you cannot bring reference materials. Practicing under the same conditions, timed and without notes, helps you get used to the pace you need to answer every question in time.
You need 75% to pass. ACAC sets this cut score with the Modified Angoff method, which is based on what a minimally qualified candidate should know. Exams are graded electronically, so you see your score right away instead of waiting for results by mail.
You qualify with a 2-year post-secondary degree (or its equivalent) plus 1 year of microbial sampling experience, or with no degree and 2 years of that experience. After you apply, you have up to 90 days to finish the application process. Check the ACAC handbook for how to document your experience.
Yes. The exam is computer-based and taken in the presence of a proctor. You can take it at a testing facility or through online proctoring. Either way, it is closed-book with the same 3-hour limit, so plan for a quiet, uninterrupted session if you test online.
You can retest whenever you are ready by calling the ACAC office to schedule. Each re-examination costs $100. Before you book, look at which topics cost you the most points and work through the matching practice sets so the retake goes better.
ACAC certifications are current for 2 years from the date of issue. To renew, you need to earn 40 Re-certification Credits every 2 years. Keeping a running record of your credits makes renewal easier. Also, ACAC certification is separate from any state mold license you may need.
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