Negative marking: the attempt arithmetic
Attempts, accuracy and your exam's scheme in; expected score, the break-even threshold and the real cost of guessing out. Set the scheme to your exam's official pattern.
Your inputs
Defaults follow the common +4/−1 objective pattern. Your exam's actual scheme lives in its official brochure; set it here before trusting any number.
The expected outcome
The three numbers that decide attempt strategy
First, break-even accuracy: penalty ÷ (reward + penalty). On +4/−1 that is 20%, exactly a five-option blind guess. That is why pure guessing is a coin-flip and any elimination tilts the odds. Second, the expected value of one attempt at your accuracy: at 80% on +4/−1, each attempt averages +3.0 marks, so leaving a confident question blank costs three marks on average. Third, the marginal attempt: the question is never whether to attempt in general but whether to attempt the next, shakiest question, and that decision should be made at your marginal accuracy, not your overall one.
Mock analysis is where this arithmetic becomes personal: your real accuracy per subject and per difficulty band, measured across timed tests, replaces guessed inputs with evidence. That measurement loop is what PrepWise practice tests run automatically, and the mock analysis guide shows the method by hand.
A worked example
Two aspirants sit the same 90-question, +4/−1 paper. A attempts 88 at 70% accuracy: about 62 correct and 26 wrong, an expected 246 − 26 ≈ 220. B attempts 72 at 85%: about 61 correct, 11 wrong, expected 244 − 11 ≈ 233. B answered sixteen fewer questions and expects a higher score, because the last sixteen attempts A made were below break-even quality. That is the entire case for skip discipline, made in one subtraction.
Averages, not guarantees; single papers vary. Verify your exam's current scheme in its official brochure.
Frequently asked questions
What is the break-even accuracy under negative marking?
The accuracy at which attempting scores exactly zero on average: penalty divided by (reward plus penalty). On the common +4/−1 pattern that is 20%, meaning pure five-option guessing is break-even and any elimination pushes attempting into profit. Set your own scheme in the calculator; the threshold moves with it.
Should I attempt a question I can narrow to two options?
On +4/−1, a 50% shot averages +1.5 marks per attempt, clearly worth taking. The calculator's expected-value line shows the arithmetic for your scheme. The skill worth drilling is recognising which questions you have genuinely narrowed and which you are merely hoping about.
Does this predict my actual exam score?
No; it computes the average outcome of an attempt strategy, which is a different and more useful thing. Real papers vary around the average. Use it to set strategy and to understand your mock results, and verify your exam's current marking scheme in its official brochure, since schemes differ and change.
Strategy from evidence, not nerves.
PrepWise measures your real accuracy per subject and drills the attempt discipline.
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