How Predictive Is Free 120 for Step 2 CK?
Free 120 has been submitted to Predict My Step Score 56,419 times and tracked against the real Step 2 CK results students went on to report. In that data, Free 120 showed moderate predictive power: a clear link to the real score, with plenty of individual variation.
What is Free 120?
The Free 120 (Free 137 for Step 3) is the USMLE's own free set of sample questions, published to show what the exam interface, question style and pacing feel like. It reports a raw percentage correct, not a scaled score, and was never built as a score predictor — but because the questions come from the exam's authors, many students treat it as a final checkpoint.
What is a good Free 120 score?
In our data, Free 120 scores ranged from 53% to 96%. The link is real but loose: two students with the same Free 120 score can finish well apart on the real exam. A "good" Free 120 score is one that puts your likely outcome comfortably above the score you need — run it through the predictor to see where you stand.
When should you take Free 120?
Take it in the final week, mainly to rehearse the real interface and pacing, and treat the percentage as a floor rather than a forecast.
Does it matter when you take Free 120?
Timing matters twice over. First, a score from six weeks out is a snapshot of a student who then kept studying, so early tests tend to sit below the real result — much of what looks like "underprediction" is simply improvement after the test. Second, our predictor does not treat every score you enter equally: each one is weighted by the exam's R² and by how recently you took it, with a recency factor that decays exponentially from your most recent test back to your oldest, and your three most recent scores drive the final adjustment. Enter the days-before-exam for each test honestly — it changes the answer.
Enter your Free 120 score
How Free 120 compares
Wondering whether to take Free 120 next? See which practice tests are most predictive.
| Rank | Practice exam | Predictive power |
|---|---|---|
| 1 | NBME 16 | High |
| — | Free 120 | Moderate |
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Some practice tests miss your real score by 15+ points. Don't find out which ones on exam day.
Unlock the full ranking + your predicted scoreFrequently asked
Is Free 120 accurate?
Free 120 showed moderate predictive power in our data: a clear link to the real score, with plenty of individual variation. But no practice test is "accurate" on its own — most are taken while you are still improving, so the number you see is rarely the number you get. Combining your scores, weighted by each exam's track record and timing, gives a sharper answer than any single test. Predict your Step 2 CK score →
Does Free 120 overpredict or underpredict Step 2 CK?
Free 120 is reported as a percentage rather than a 3-digit score, so there is no direct over/under-prediction figure. Its overall predictive power in our data is moderate.
Is Free 120 or NBME 16 more predictive?
NBME 16 is more predictive in our data. The exact gap is part of the full ranking, which is available to premium users.
Where does this data come from?
56,419 Free 120 scores have been submitted to Predict My Step Score so far. Whenever a student also reports their actual Step 2 CK result, the pair goes into the model behind this page; it was last refit on 2026-05-14.
Can't I just ask ChatGPT how predictive Free 120 is?
Not reliably. A prediction is only as good as the paired data behind it: real Free 120 scores matched to the real Step 2 CK result those same students went on to get. General-purpose AI models are trained on forum posts and articles, not on verified outcomes, so what you get back is a summary of anecdotes rather than a calibrated estimate. The numbers on this page come from students who reported both. Read more →
Free 120 alone gives you a blurry answer. Your full set of scores gives a sharp one.
The predictor combines every practice exam you have taken — weighted by how predictive each one is and how recently you took it — into a single prediction with a 95% confidence interval.
Predict my Step 2 CK scorePremium adds the full ranking, unlimited predictions, and tracking over time.
Data refreshed 2026-05-14.
