Turn the number of wrong answers into a percentage grade.
The base calculation is points earned divided by points possible, multiplied by 100. A score of 43 out of 50 is 86 percent.
Letter grade boundaries vary between institutions, but the most common US scale is A at 90 and above, B at 80, C at 70, D at 60, and F below that. Some schools use a stricter seven-point scale where an A begins at 93. Always check the syllabus rather than assuming.
Most courses weight assessment categories differently — homework 20 percent, midterm 30 percent, final 50 percent, for example. The final grade is the weighted average of category percentages, not of raw points.
Final = Σ (category percentage × category weight)
This has a practical implication students often miss: a perfect score on a small-weight assignment moves the final grade very little, while a poor score on a heavily weighted final can dominate everything that came before. Working out where the weight actually sits, early in the term, tells you where effort pays.
The most useful version of this calculation runs backwards: given your current standing, what score does the final exam require to reach a target grade?
Required = (target − current × (1 − final weight)) ÷ final weight
If you hold 82 percent going in, the final is worth 40 percent, and you want 90 overall, you need (90 − 82 × 0.6) ÷ 0.4 = 102 percent — which tells you the target is out of reach without extra credit. Running this early is more useful than running it the night before.
Curving adjusts grades relative to class performance. A simple curve adds a fixed number of points; a normalised curve maps scores onto a target distribution, which can mean a high raw score still receives a middling grade if the class performed well overall.
Many courses drop the lowest score in a category. This is worth understanding: it means one bad week is usually absorbed, but skipping deliberately to use the drop leaves no margin if illness strikes later.