Weighted Average: How to Calculate a Course Grade From Categories
October 21, 2026
A weighted average multiplies each score by its weight, then adds the results. If exams count for 40%, homework for 30%, and the project for 30%, scores of 85, 92, and 78 give 0.40 × 85 + 0.30 × 92 + 0.30 × 78 = 34 + 27.6 + 23.4 = 85.0. A simple average of the same three scores would be 85.0 too in this case, but only by coincidence, since the weights differ.
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Convert each percentage weight to a decimal, so that the weights add to 1. Multiply every score by its weight, then add the products. If the weights do not add to 1 (or 100%), divide the sum by the total weight.
Example: homework counts 30% and averages 92, which contributes 27.6 points. The project contributes 23.4 points, and the exams contribute 34. The total is 85.0.
| Category | Weight | Score | Contribution |
|---|---|---|---|
| Exams | 40% | 85 | 34.0 |
| Homework | 30% | 92 | 27.6 |
| Project | 30% | 78 | 23.4 |
| Total | 100% | 85.0 |
Finding the Score You Need
Suppose the final exam is 40% of the grade and you currently have 82% across the other 60% of the course (which contributes 0.60 × 82 = 49.2 points). To finish with 85, you need 85 − 49.2 = 35.8 points from the final, so a score of 35.8 ÷ 0.40 = 89.5 on the exam.
Always check whether the target is achievable: if the required score is above 100, it is not, and an alternative such as extra credit or a lower target is needed.
Common Pitfalls
Averaging category averages is only correct if you apply the weights. Averaging every assignment equally gives a different answer when categories contain different numbers of items. Some courses also drop the lowest score in a category, which should be applied before weighting.
Check the syllabus for rounding rules, since 89.5 may or may not count as 90 for a letter grade.
Frequently Asked Questions
How do I calculate a weighted average?
Multiply each value by its weight, add the products, and divide by the sum of the weights.
What if weights don't add up to 100%?
Divide the weighted sum by the total of the weights.
How do I find the exam score I need for a target grade?
Subtract the points already earned from the target and divide by the exam's weight.
Is the weighted average the same as the mean?
Only if all weights are equal.