Test planning · 4 min read
How many questions can I miss and still pass a test?
Find the maximum wrong answers for a target percentage on an equally weighted test, with examples for 20, 25, 30, and 50 questions.
By Best Grade · Worked examples using the formulas in our calculators
The short answer
On an equally weighted test without partial credit, multiply the number of questions by your target percentage as a decimal and round up to the next whole correct answer. Subtract that minimum correct count from the total. For 25 questions and an 80% target, you need 20 correct and can miss at most 5.
The maximum-wrong-answers formula
Let N be the total number of questions and P be the target percentage. The minimum correct count is N × P ÷ 100 rounded upward to a whole number. Maximum wrong answers is N minus that count. Rounding up matters because you cannot answer a fraction of a question correctly in this whole-question model. This assumes equal points per question, no penalty for wrong answers, no partial credit, and a target between 0% and 100%.
Maximum wrong = N − ceiling(N × target % ÷ 100)
Example: how many can I miss on a 25-question test?
For an 80% target, 25 × 0.80 = 20 correct answers, so you can miss 25 − 20 = 5. For a 90% target, 25 × 0.90 = 22.5. Round up to 23 correct answers, leaving at most 2 wrong. That gives 23/25 = 92%. Three wrong would leave 22 correct, or 88%, which does not reach 90%. Rounding 22.5 down would give the wrong limit.
Quick reference for 70%, 80%, and 90% targets
On 20 questions, you can miss at most 6 for 70%, 4 for 80%, or 2 for 90%. On 25 questions, the limits are 7, 5, and 2. On 30 questions, the limits are 9, 6, and 3. On 50 questions, the limits are 15, 10, and 5. Each limit reaches at least the stated target before display rounding. Your passing score may be different, so use the percentage in your syllabus rather than assuming 70% is always enough.
What if the target is a letter grade?
First look up the minimum percentage for that letter in your actual grading scale. Best Grade's default example scale begins A at 93%, while A− begins at 90%. On a 20-question test, reaching 93% requires 19 correct, or 95%, so you can miss only 1. Reaching 90% requires 18 correct, so you can miss 2. A custom scale could change both answers. A displayed rounded score is not automatically the score a teacher uses to assign a letter.
Unequal points and partial credit need a different approach
If questions have different point values, count points rather than questions. On a 100-point test with an 80% target, you may lose at most 20 points. That could mean four missed 5-point questions or twenty missed 1-point questions; there is no single question limit without knowing the point distribution. With partial credit, subtract the actual points lost, not the number of questions with any mistake. Use the points calculator to combine the earned and possible amounts.
Does this work for standardized or scaled-score exams?
Not necessarily. Some exams use scaled scores, penalties, adaptive question difficulty, or other scoring rules. A target scaled score cannot be converted into a fixed number of missed questions with this percentage formula. Use the exam provider's published scoring guidance. This guide is for classroom-style percentage grading, not a prediction of GRE, SAT, or another standardized exam result.
Can I use this to plan a final exam?
Yes, if you already know the required exam percentage and the exam follows these assumptions. First calculate the final exam percentage needed from your current course average, target course grade, and final weight. Then convert that exam percentage to a minimum correct count. If the required exam percentage is above 100%, an ordinary test capped at 100% cannot meet the target. A teacher's extra-credit or minimum-exam rules must be considered separately.
References & grading assumptions
Examples are illustrative, not a school policy. Consult your syllabus for your actual grading rules.
CalculatorSoup: percentage relationships and formulas