Questions You Can Miss on the CDL Permit Test: 80% Rule

You can miss 1 in every 5 questions. Federal rule 49 CFR 383.135 says you must answer at least 80 percent correctly on each knowledge test. That is 10 misses on a 50-question test and 4 misses on a 20-question test. FirstTry CDL built the table below so you can find your number. To see what 80% means, first check how many questions are on each test in your state.

The rule in plain words

The federal text reads: "To achieve a passing score on each of the knowledge tests, a driver applicant must correctly answer at least 80 percent of the questions." Source: 49 CFR 383.135.

The rule says "each." You do not average your tests together.

Most you can miss at 80%

The math is simple. Take 20 percent of the question count. Your state decides how many questions are on each test. The federal rule does not set a count.

What states publish

These are counts and pass marks from official state pages. Each was checked on the date shown.

Michigan's 56 and 14 come from our math on its 70 questions and 80 percent rule. Michigan Group B and C tests have 50 questions. Iowa prints "questions and number you may miss" in its Quick Guide, such as 50 and 10.

Where the pass mark is different

Illinois says its School Bus test needs 90 percent. Every other Illinois CDL knowledge test needs 80 percent (Illinois SOS). On a 20-question test, 90 percent means you can miss only 2.

Check your own manual. A state can set a higher bar than the federal 80 percent. For the pass mark, question count and retake wait in each state, see the CDL permit test facts by state.

Each test stands alone

General knowledge, air brakes, combination and every endorsement is a separate test. Each one has its own score. If you pass general knowledge but miss the mark on tanker, you retake tanker only. Waits and fees vary, so see what to do after failing the CDL permit test.

Three tips from us

These are our study advice, not rules.

1. Protect air brakes and combination first. The federal rule says a driver who scores under 80 percent on air brakes can be issued a permit with an air brake restriction. A driver who fails combination must not be issued a Group A permit. Those two tests cost you the most if you miss.
2. Spend your misses by test size. On a 20-question test you only get 4. Skip risky guessing there. On a 50-question test you get 10, so one weak topic will not sink you if the rest is solid.
3. Aim above the line. Treat 85 percent as your practice goal, not 80. On test day you will be nervous and one tricky question can cost you, so build a cushion before you book.

Want to see where you stand? Try these 10 exam-style questions built from the official CDL manual.