"Weights" cause more grade confusion than any other topic, because one word is used for four different things: category weights inside a course, weighted vs unweighted course grades, drop-lowest rules, and weighted GPA at school level. Here is each one, plainly.
1. Category weights inside a course
Most syllabi split your grade into categories — say homework 20%, quizzes 20%, exams 60%. Your course grade is each category average multiplied by its weight, added together. An 80 in exams moves your grade three times as much as an 80 in homework. Two students with the same raw average can finish with different grades if their marks sit in different categories.
2. Grade so far, when weights don't add to 100
Halfway through a course, only some categories are graded. If exams (60%) are at 80 and nothing else is marked yet, your grade so far is 80 — the completed weight is renormalised to 100%. A good calculator shows this figure and a projection, rather than pretending the unmarked 40% is zero.
3. Drop-lowest rules
Many courses drop your lowest quiz or homework score. This changes the category average before the weight is applied: scores of 50, 90 and 100 average 80, but with the lowest dropped they average 95. Always check whether your syllabus offers this before panicking about one bad quiz.
4. Weighted vs unweighted GPA (school level)
Separately, high schools report GPA on an unweighted 4.0 scale, or a weighted scale (often 5.0) that adds a bonus for honours and AP classes. Colleges typically look at both, or recalculate their own. This is a school-reporting choice — it is not the same thing as category weights inside a single course.
Worked example
Homework average 95 (weight 20), quizzes 85 (weight 30), exams 78 (weight 50):
(95 × 20 + 85 × 30 + 78 × 50) ÷ 100 = (1900 + 2550 + 3900) ÷ 100 = 83.5
The unweighted average of the three category scores would be 86 — flattering, and wrong.
Try it
Run your own categories, points or a semester split in the Weighted Grade Calculator, and see how semester splits like 40/40/20 apply the same idea at term level.