Test score calculator

The basic calculation

Percentage is correct divided by total, times 100. Forty-two out of fifty is 84%. That much is obvious, but two things around it are not: how the percentage maps to a letter, and how many you could have missed and still hit your target.

Grade boundaries are not universal

The familiar 90/80/70/60 scale is a US convention and not a law of nature. Plenty of institutions set different cut-offs, and some subjects use scales where 70% is an outstanding result.

UK degree classification is the clearest example of the difference. A First is 70% and above, an Upper Second 60-69%, a Lower Second 50-59%, and a Third 40-49%. A score of 72% is a mediocre C on the US scale and a First-class result in the UK system. Neither is wrong; they are simply different mappings.

Always check your own syllabus. The scale option here covers the common cases, but a course-specific boundary beats any default.

Negative marking

Some exams — several professional certifications, and historically the SAT — deduct marks for wrong answers to discourage blind guessing. With a penalty of 0.25 per wrong answer, getting 42 of 50 right gives 42 − (8 × 0.25) = 40 marks, or 80% rather than 84%.

Where negative marking exists, the guessing calculation changes. With a 0.25 penalty on a five-option question, random guessing has an expected value of exactly zero — you gain 1 mark a fifth of the time and lose 0.25 four-fifths of the time. Eliminating even one option makes guessing positive-value again. With no penalty, you should always answer everything.

Working backwards from a target

The more useful direction is often the reverse: how many can I afford to get wrong? For 80% of 50 questions you need 40 correct, so you can miss 10. Knowing that before an exam changes how you allocate time — it tells you when to move on from a question rather than sinking five minutes into it.

Note the rounding. Needing 39.2 questions means needing 40, because you cannot answer four-fifths of a question. The calculator rounds up for exactly that reason, so the target is always genuinely achievable.

Partial credit and weighted questions

This assumes every question is worth the same. If your exam has a 20-mark essay alongside 30 one-mark questions, enter marks rather than question counts — 42 marks out of 50 works the same way regardless of how those marks were distributed.

For a whole course made of several weighted components, this is the wrong tool: use a weighted grade calculator, which handles each assessment's contribution separately.

Common questions