Best Step 2 CK score predictor: head-to-head on real scores
Plenty of tools promise to predict your Step 2 CK score. This page measures them all the same way: each tool's predictions checked against real, self-reported outcomes from r/Step2 score releases, with the same error metrics for every row. No stars, no sponsorships, just measured error.
| Predictor | Median error | Average error | Within 5 | Within 10 | Tendency |
|---|---|---|---|---|---|
| This tool | ~4 pts | ~5.1 pts | 59% | 88% | unbiased (~0.4) |
| AMBOSS prediction* | ~5 pts | ~6.0 pts | 53% | 83% | underpredicts by ~4 |
| "NBME average + 13" rule† | ~5 pts | ~6.0 pts | 52% | 83% | overpredicts by ~1 |
| PMSS and others‡ | ~6 pts | ~6.9 pts | 47% | 77% | underpredicts by ~5 |
| r/Step2 calculator§ | ~7 pts | ~7.3 pts | 41% | 71% | underpredicts by ~6 |
| usmlepredictor.com | ~9 pts | ~10 pts | 25% | 58% | underpredicts by ~9 |
* In its own published validation, AMBOSS reports a typical error of 7.6 points for its score predictor. The row above reflects AMBOSS predictions that students actually posted alongside their results.
† Works for the middle of the pack, breaks at the edges: below an NBME average of 235 the rule underpredicts by ~5 points, above 255 it overpredicts by ~6, and it misses by 15+ points more than twice as often as the model on this site.
‡ Most people post their predicted score without naming the tool that produced it. Many likely come from PMSS, but the source can't be confirmed, so all unattributed predictions are pooled.
§ Last updated in 2022; accepts nothing newer than NBME 12.
Median error: half of predictions were closer than this. Average error: the mean absolute miss. Last benchmarked June 2026; full methodology on the how-it-works page.
The short version: the model on this site measured most accurate on every metric, AMBOSS and the NBME-average rule are reasonable backups in the middle of the score range, and the two oldest tools now underpredict recent exams by 6–9 points.
The tools, one by one
This site's predictor
Trained on 2,200+ real score reports and validated with a chronological blind test: the model saw only reports posted before 2025, then predicted 481 exams from 2025-2026 it had never seen. Median miss ~4 points, 88% within 10, essentially zero bias, with calibrated probability ranges. It runs free in your browser and uses every practice test you have, including timing.
AMBOSS score prediction
The strongest third-party option measured: median ~5 points on 252 posted predictions, with a consistent tendency to underpredict by ~4. It requires an AMBOSS account and uses your self-assessment plus qbank performance.
"NBME average + 13"
The best simple rule found in this data: average your NBME scores and add 13. Surprisingly competitive in the middle of the score range and free by definition, but it has no concept of recency or test mix, underpredicts low scorers by ~5, overpredicts high scorers by ~6, and misses badly more than twice as often as a real model.
PMSS and other posted predictions
Pooled predictions with no named source, many likely from PMSS: median ~6 points and an average of ~6.9, underpredicting by ~5 on recent exams.
r/Step2 community calculator
A community favorite from 2021-2022 that has not been updated since: it accepts nothing newer than NBME 12. In 120 fresh runs against 2025-2026 outcomes it averaged ~7.3 points of error and underpredicted by ~6. Fine historically; outdated today.
usmlepredictor.com
Measured on the same 481-exam holdout using its own published in-browser algorithm (verified to reproduce the live site's outputs exactly): median miss ~9 points, average ~10, and a systematic underprediction of ~9 points. Its predictions sat at the bottom of every accuracy metric in this comparison.
What actually makes a predictor accurate
Four things separated the top of the table from the bottom: recent training data (the exam and its forms drift, which is what sank the 2022-era calculator), using multiple inputs instead of one test, honest calibration (a tendency to under- or over-predict by 4-9 points is a bigger practical problem than a wide error bar), and blind testing on outcomes the model never saw. Ask any predictor for those four things; the numbers above are what they look like when published.
Common questions
What is the most accurate Step 2 CK score predictor?
Measured against real exam outcomes, the predictor on this site had the lowest error: a median miss of about 4 points and 88% within 10 points on a blind test of 481 exams from 2025–2026. AMBOSS predictions and a simple NBME-average rule came next at about 6 points of average error. There is also a hard limit no predictor can beat: USMLE reports a standard error of about 7 points on Step 2 itself, meaning the same student could score several points differently on a different day. That randomness puts a floor of roughly 5–6 points on the average error any tool could ever achieve, and this predictor's 5.1 sits essentially at it. Past this point, better predictions are mathematically impossible; the remaining error is the exam's, not the model's.
How accurate is the AMBOSS Step 2 predictor?
On 252 AMBOSS predictions that students posted alongside their real results, the median miss was about 5 points and the average about 6, with a tendency to underpredict by ~4 points. In its own published validation, AMBOSS reports a typical error of 7.6 points.
Is the r/Step2 community calculator still accurate?
It was solid in its era, but it was last updated in 2022 and accepts nothing newer than NBME 12. In 120 fresh runs against 2025–2026 exams it averaged about 7.3 points of error and underpredicted by ~6.
Can any predictor be exact?
No. USMLE reports a standard error of about 7 points for Step 2 CK itself, which puts a floor of roughly 5–6 points on the average error any predictor could achieve. Treat every prediction as an estimate, not a guarantee.
Get a real prediction, not a rule of thumb
The full predictor combines all of your practice tests with their timing, shows calibrated probability ranges, and was the most accurate of every predictor tested against real scores. See the head-to-head comparison.