How Many Questions Can I Miss?

How the "how many can I miss" math works

It is two steps, and almost everyone gets the second one wrong. First, work out how many questions you need to get right: total questions x target percentage. Second, subtract that from the total: total questions - questions you need right = questions you can miss.

So on a 50-question test where you need 80%: 50 x 0.80 = 40 correct, and 50 - 40 = 10 wrong allowed. On a 100-question test at 90%: 90 correct, 10 wrong. Simple enough.

The catch is rounding. If the answer is not a whole number, you must round the required correct answers up, never down. A 47-question test at 80% gives 37.6, you need 38 right, so you can only miss 9. Round 37.6 down to 37 and you would think 10 wrong answers still passes; it does not, because 37 out of 47 is only 78.7%. The calculator above always rounds the required score up, which is the safe direction.

One more thing worth knowing: some teachers and some testing companies round the final percentage rather than the raw score. A 79.5% might be recorded as 80%. That is a grading policy, not arithmetic, so ask before you count on it. The National Center for Education Statistics collects grading-scale data if you are curious how much scales vary between schools.

Worked example: 50 questions, 80% needed

This is the most common shape for a classroom test. Here is the full working.

• Questions you must get right: 50 x 0.80 = 40
• Questions you can miss: 50 - 40 = 10
• Your score if you miss exactly 10: 40 / 50 = 80.0%
• Your score if you miss 11: 39 / 50 = 78.0%, a fail on an 80% threshold
• Your score if you miss 5: 45 / 50 = 90.0%

Notice how tight the margin is near the line. One extra wrong answer takes you from a comfortable pass to a fail, because each question is worth a full 2%. If you are aiming for a B- at 80%, you are aiming to be at least 10 questions from the edge.

Now flip it around. Suppose you have already taken the test and know you missed 7. You got 43 right, which is 43 / 50 = 86.0%, a solid B. Knowing the number you can miss is useful before the test; knowing the number you did miss is useful after it.

Worked example: a 40-question quiz at 70%

Quizzes usually carry a lower bar. Take a 40-question quiz with a 70% pass mark.

• Required correct: 40 x 0.70 = 28
• You can miss: 40 - 28 = 12
• Score if you miss 12: 28 / 40 = 70.0%
• Score if you miss 8: 32 / 40 = 80.0%
• Score if you miss 16: 24 / 40 = 60.0%

Twelve wrong answers out of forty is a real cushion, you can miss nearly a third of the quiz and still pass. On the 50-question test above you could only miss a fifth. Same idea, different pressure.

This is the practical value of the calculator: it converts an abstract percentage into a concrete budget. "I need 70%" is hard to hold in your head during an exam. "I can miss twelve" is something you can track as you go, and it tells you when to slow down and check your work.

How many you can miss on common test sizes

The table below shows the number of wrong answers you can afford on tests of different lengths. Read across to find your target percentage.

Two patterns jump out. First, on short tests the numbers are chunky: on a 10-question quiz at 80% you can only miss 2, and one careless slip is 10% of your grade. On a 100-question test at 80% you can miss 20, and a slip barely registers. Longer tests are more forgiving of individual mistakes.

Second, the difference between 70% and 80% is not one question, it is several. On a 50-question test it is 5 questions, or 10% of the test. If you are between two grade bands, the gap is usually bigger than students expect, and it is worth a few minutes of extra review.

Why rounding matters more than you think

Almost every wrong answer to "how many can I miss" comes from rounding in the wrong direction. Here is the rule stated plainly: round the required correct answers up to the next whole question, then subtract.

Walk through a 47-question test at 80%. 47 x 0.80 = 37.6. You cannot answer 0.6 of a question, so 37 correct is not enough, 37 / 47 is 78.7%, a fail. You need 38, which is 80.9%. So you can miss 47 - 38 = 9. If you had rounded 37.6 down to 37, you would have concluded you could miss 10, and you would have been wrong by one question.

The same trap shows up with 25-question tests. 25 x 0.90 = 22.5, so you need 23 right and can miss 2, not 3. With 30 questions at 70%, 30 x 0.7 = 21 exactly, so no rounding is needed and you can miss 9. When the target percentage divides cleanly into the number of questions, the arithmetic is exact; when it does not, round up and stay safe.

Passing scores on real exams

Real tests rarely use a flat 70%. Here are the pass marks that come up most often, and what they mean in wrong answers.

Notice the last row. Some professional exams do not use a raw percentage at all, they scale your score against the difficulty of the questions you received, so two candidates who got the same number wrong can get different results. If you are sitting one of those, a raw-percentage calculator gives you a rough guide only. State education agencies such as the Texas Education Agency publish the cut scores for their own assessments, and the US Department of Education links to state-by-state requirements.

How to use this while you study

The number you can miss is not just trivia for the exam hall, it changes how you prepare. If you can miss 10 out of 50, you do not need to master every topic. You need to be solid on the material that shows up most, and confident enough to skip the one question that is eating your time.

A practical method: take a practice test, count your wrong answers, and compare that to your budget. If you missed 14 and your budget is 10, you know you are four questions short and you know roughly which topics they came from. That is far more actionable than "I got a C".

In the exam itself, the budget is a pacing tool. If you can miss 10 and you hit a question you genuinely cannot answer, the rational move is to guess, mark it, and move on rather than burn five minutes. Ten wrong answers is a pass; two unanswered questions because you ran out of time is not.

One caution: do not aim for the budget. Aim for a comfortable margin above it. The number of questions you can miss is the edge of a cliff, not a target, and exams have a way of including two or three questions you have never seen before.