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Within one conversation with him, my score managed to jump up 7 points on my practice step 1 exam (CBSSA).
Cole D.
The NBME CBSE (Comprehensive Basic Science Exam) is a 200-question test of Step 1 content that your medical school gives you, usually to judge whether you are ready for USMLE Step 1 (NBME Comprehensive Subject Exams). You cannot buy it yourself, and NBME sets no passing score for it; your school decides what result it expects (NBME score guide).
This page covers the CBSE's format and content, how the score and the Step 1 estimate on your report are calculated, how it differs from the self-assessment students buy, and how to prepare.
Official practice exams
| Topic | Official rule | Source |
|---|---|---|
| Version you can buy (CBSSA) | Comprehensive Basic Science Self-Assessment: seven forms, from $62, four sections of 50 questions at 1 hour 15 minutes each (standard-paced), with an estimated probability of passing Step 1. | NBME: Comprehensive Basic Science Self-Assessment |
| Passing score | NBME sets none. It advises schools to use subject exam scores together with other measures of performance, not alone, when deciding grades. | NBME: CBSE score interpretation guide |
| Results | Results go to your school first; NBME emails you about your reports in INSIGHTS 3 to 4 calendar days after the school receives them. | NBME: CBSE score interpretation guide |
What the CBSE is, and who gives it
The CBSE is one of NBME's Comprehensive Subject Exams. Schools use them to measure progress and readiness for Step 1 and Step 2 and administer them securely, and NBME is explicit that they are not meant for practice (NBME). Subject exams are sold to medical school faculty only (NBME common questions), which is why there is no way to register for a CBSE on your own.
Your school pays the fee: $62 per examinee when it gives the exam on campus, $152 when you sit it at a Prometric center (NBME fees). Dates are set by your school, so the answer to "when is the CBSE" lives in your curriculum calendar, not on NBME's site.
CBSE format and content
The exam is 200 questions in 5 hours 15 minutes, including a 15-minute optional break, plus a 15-minute tutorial when it is given on the web (NBME timing chart). NBME describes it as an integrated test of basic science with somewhat more weight on second-year courses, built to reflect Step 1 content and to use the same item formats (NBME content outline).
| System | Share of exam |
|---|---|
| Reproductive and endocrine systems | 12-16% |
| Respiratory and renal/urinary systems | 11-15% |
| Behavioral health and nervous systems/special senses | 10-14% |
| Blood and lymphoreticular/immune systems | 9-13% |
| Musculoskeletal, skin and subcutaneous tissue | 8-12% |
| Multisystem processes and disorders | 8-12% |
| Cardiovascular system | 7-11% |
| Gastrointestinal system | 6-10% |
| Social sciences: communication and interpersonal skills | 6-9% |
| Biostatistics and epidemiology/population health | 4-6% |
| Human development | 1-3% |
By task, 60-70% of questions ask you to apply foundational science, 20-25% are diagnosis, 6-9% communication and interpersonal skills, and 4-6% practice-based learning. Foundational science is spread through the organ systems rather than tested as separate subjects, so pharmacology or microbiology shows up inside a cardiology or renal vignette.
How the CBSE is scored
Since February 2022 the CBSE reports equated percent correct (EPC) scores: the percentage of the whole content domain you would be expected to answer correctly at your level, adjusted so that harder and easier forms give comparable scores (NBME score guide). An EPC of 70 means about 70% of the content mastered, not a place on a curve.
The total score has a standard error of 4 points. If you retested without learning or forgetting anything, your score would land within 4 points of the first one about two-thirds of the time. Content-area scores are less precise than that, so treat a single weak area as a lead to check against your question bank, not a verdict.
Your Examinee Performance Report also gives an estimated probability of passing Step 1 if you tested within a week, and marks each content area as lower than, about the same as, or higher than recent Step 1 first-takers from LCME-accredited schools (NBME score guide).
What is a good CBSE score?
NBME does not publish one. It gives no passing score and asks schools to combine subject exam results with other measures rather than use them alone (NBME). In practice, the number that matters is the one your school uses. If your school treats the CBSE as a checkpoint before it lets you sit Step 1, ask for the exact rule in writing: the score, how many attempts, and when.
For your own planning, the more useful line on the report is the Step 1 pass probability, because it is tied to the exam you actually need to pass. Step 1 itself is pass/fail; in 2025, 93% of first takers from US MD schools and 89% from US DO schools passed (USMLE performance data). A CBSE that puts your probability well below comfortable is a reason to move the Step 1 date, not to sit it and hope.
CBSE vs CBSSA: the school exam and the one you buy
Students often say "NBME" for both, but they are different products. The CBSSA is the Comprehensive Basic Science Self-Assessment, which you buy and take at home (NBME CBSSA).
| Feature | CBSE | CBSSA |
|---|---|---|
| Who arranges it | Your school | You |
| Length | 200 questions, 5 h 15 min | Four sections of 50 questions, 1 h 15 min each standard-paced |
| Cost | Paid by the school ($62 on campus, $152 at Prometric) | From $62 per form, seven forms |
| Purpose | Secure readiness check; not for practice | Practice and progress tracking |
| Step 1 estimate | Estimated probability of passing | Estimated probability of passing |
Because both report a Step 1 pass probability on the EPC scale, a CBSSA a few weeks before your school's CBSE is a reasonable rehearsal. Use a form you have not seen.
How to prepare for the CBSE
Treat it as a Step 1 checkpoint, because that is how NBME builds it. What works for the people we tutor:
- Practise integrated questions, not subject reviews. With foundational science spread through the systems (NBME), a pharmacology chapter read on its own does less than mixed system blocks.
- Weight your time to the outline. Reproductive and endocrine, respiratory and renal, and behavioral health and neuro together make up roughly a third or more of the exam.
- Do not skip communication and biostatistics. Together they are 10-15%, and they are among the fastest points to recover.
- Sit one timed full-length first. Five hours of questions is long. A timed CBSSA tells you whether stamina or knowledge is the bigger problem.
- Read the report by area, then check it. A weak area on the CBSE should match what your question bank shows before you rebuild your plan around it.
Help after a low CBSE
A low CBSE is usually the moment to rebuild the plan, not to add more hours to it. Our Step 1 tutors include Dr. Sean Moazezi, DO, Dr. Sahith Valluru, Chelsi Flippo, MD, Alexandra Llovet and Dante Magdici. In sessions you work live questions while the tutor checks how you read the stem and which clue you used, and the plan is built from your CBSE report and question bank data.
See how Step 1 tutoring works, or read our Step 1 study schedule for how a dedicated period is laid out.
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