Why a Weighted Final Grade Isn't a Simple Average
Published 2026-10-04
A tempting shortcut that gives the wrong number
Add up a 90% quiz average and an 80% final exam score and divide by two, and you get 85% — but that's only correct if the quiz and final were worth exactly the same share of the grade. Most syllabi weight them very differently, which means a plain average silently gives the wrong final grade.
What weighting actually does
Weighted grading multiplies each category's score by its share of the total grade before adding anything together: Final Grade = Σ(Score × Weight) ÷ Total Weight. A 50%-weighted final exam has five times the pull on your final grade that a 10%-weighted quiz category does, exactly matching what the syllabus intends.
Why the weights should add to 100
If a course's categories only add up to 90% total weight (a common oversight when a grade calculator is built before every category is finalized), the formula still runs, but it's implicitly assuming the missing 10% doesn't exist yet — worth double-checking your weights sum to 100% once everything is graded.
Calculate yours
Our Grade Calculator lets you add a row per graded category with its own score and weight, and does the weighted math instantly as you type.