// tutorial
How weighted grades work. Three examples from simple to messy.
Weighted grades assign different importance to different assignments. A final exam worth 30% has three times the impact of a quiz worth 10%. This page walks through three increasingly complex examples so you can compute any class by hand.
Updated 28 April 2026
The formula
avg = (g1 x w1 + g2 x w2 + ... + gN x wN) / (w1 + w2 + ... + wN)
When all weights add up to 100% (1.0), the denominator is 1 and you can skip the division. When only some assignments are complete, divide by the sum of completed weights to get your current average.
Example 1 / simple
3 categories, all complete
Biology 101. Exams 50%, Labs 30%, Homework 20%. Everything done.
Weights total 100%, so just add the weighted values: 41.0 + 27.3 + 19.0 = 87.3%. The exam average (82%) pulled the grade down because exams carry the heaviest weight at 50%. Even with 95% on homework, the overall lands at 87.3%.
Example 2 / partial
5 categories, one missing
English 200. Participation 10%, Response Papers 15%, Midterm 20%, Final Essay 30%, Presentation 25%. The final essay is not in yet.
With 70% determined, current average is 87.1%. To find what you need on the 30% final essay:
Example 3 / complex
Category averaging plus partial completion
Chemistry 301. Lab Reports 25% (6 reports), Problem Sets 20% (10 sets), Midterm 20%, Final 35%. You have 4 of 6 lab reports and 8 of 10 problem sets done.
// step 1: average within each category
Lab reports (4 of 6 done): 88, 92, 78, 85. Avg = 85.75%
Problem sets (8 of 10 done): 90, 85, 92, 88, 95, 82, 91, 87. Avg = 88.75%
Midterm: 76%
// step 2: partial weights
Lab reports: 4/6 x 25% = 16.67% weight done
Problem sets: 8/10 x 20% = 16.0% weight done
Midterm: full = 20% weight done
// step 3: weighted points
The 76% midterm is dragging the average down because it has the largest completed weight share. With the final worth 35% plus 2 lab reports and 2 problem sets remaining (about 12.33% more weight to come), roughly 47% of the grade is still up for grabs. Plenty of room to move.
Common confusion points
Why is my grade lower than the average of my scores?
Because lower scores carry more weight. If you got 95% on homework (20% weight) and 75% on the midterm (30% weight), your average is not (95+75)/2. It is (95 x 0.20 + 75 x 0.30) / 0.50 = 83.0%. The midterm pulls harder because it weighs 1.5x as much.
My weights do not add up to 100%
They should, when all assignments are listed. Check for overlaps in the syllabus (e.g. "Tests 30%" that is then split into Midterm 15% and Final 15%, same thing listed twice). If the total is genuinely 110%, that is built-in extra credit and a perfect score gives you 110%.
I got a zero. How bad is it?
Devastating. A zero contributes nothing yet still counts in the denominator. A 0% on a 5% homework costs 5 points off your final grade if you would have aced it, or about 4.25 if you would have got 85%. One missed 5% assignment hurts as much as dropping 15 points on a 30% final.