Quick answer
NBME Form 14 is currently the most predictive self-assessment for Step 2 CK: it correlates at r = 0.92 with the real exam, with 80% of predictions landing within ±5–7 points (n = 5,039 verified outcomes). Forms 14–16 are calibrated to the current item bank; older forms (9–13) typically under-predict, so treat them as a floor rather than a target.
Last updated: July 2026 · How we calculate this
Understanding NBME Form-to-Step Conversions
NBME self-assessment forms (CBSSA for Step 1, CCSSA for Step 2 CK) report your performance as an Equated Percent Correct (EPC) on a 0-100 scale plus a 3-digit equivalent that approximates current Step 2 CK scoring. NBME does not publish the official conversion tables — the values you see on your report come from their internal item-response-theory equating model.
Form-specific bias matters. Across thousands of community-reported pairs, NBME 9 systematically under-predicts the real Step 2 CK score by ~10 points, while NBME 14-16 (the newest forms) are calibrated within ~3 points of actual outcomes. Our converter applies a per-form bias correction that matches each form's empirical track record.
Days-to-exam decay. Students typically score above their NBME prediction when the practice exam was taken several weeks before the real test, because of continued study and exam-day adrenaline. We apply the Tackett 2021 decay model (PMC8368818) as a soft adjustment when you tell us how far out you are.
NBME Predictor FAQs
Why does my actual NBME report show an Equated Percent Correct?
NBME uses EPC because it is form-equated — a 70 EPC means the same content mastery whether you took Form 9 or Form 16. Raw percent correct is not comparable across forms.
Which NBME form is the most predictive?
Forms 14-16 currently. They are calibrated against the current Step 2 CK item bank. Older forms (9-13) under-predict because they were calibrated against earlier test versions.
Can I trust offline or older NBME forms?
Yes for trajectory tracking, but expect to score above their prediction. Use older forms as a floor, not a target.