Most courses are graded on weighted categories rather than a straight average: homework might count for 20%, midterms 40%, and the final 40%. Averaging every score equally will give you the wrong number, sometimes by a full letter grade, because it treats a five-point quiz as equal to a hundred-point exam.
The correct method is to work out your percentage within each category first, then multiply each by its weight and add the results. That way a perfect homework record contributes exactly the twenty points it is worth, and no more.
A worked example
| Category | Weight | Your score | Contribution |
|---|---|---|---|
| Homework | 20% | 95% | 19.0 |
| Quizzes | 15% | 88% | 13.2 |
| Midterm | 25% | 78% | 19.5 |
| Final exam | 40% | 85% | 34.0 |
| Total | 100% | — | 85.7% |
Common letter-grade cutoffs
- A: 90–100%, with A− often starting at 90 and A at 93.
- B: 80–89%.
- C: 70–79%, and typically the minimum passing grade for a course in your major.
- D: 60–69% — passing for credit at many institutions but not for prerequisites.
- F: below 60%.
- Cutoffs vary by school and sometimes by instructor; check the syllabus rather than assuming.
Details that change the result
- Dropped scores: many courses drop the lowest quiz or homework, which can be worth a percentage point or two.
- Curves: a curve applied to a category rather than the final grade behaves differently — ask which.
- Extra credit: check whether it is added to a category or to the final percentage, since the two differ by the category weight.
- Rounding: an 89.5% may or may not become an A. Departments differ, and this is worth knowing before the last assignment rather than after.
Where to spend your effort
The value of a point depends entirely on its category weight. Ten extra points on homework worth 20% of the grade moves your total by two points at most; ten points on a final worth 40% moves it by four. Work out the maximum remaining points in each category before deciding what to prioritise — it is a short calculation that frequently reverses people's instincts about what to study.