How to Calculate Weighted Grades

Weights are written as decimals in the multiplication — 20% becomes 0.20 — or you can keep them as whole numbers throughout and divide by the total at the end. Both give the same answer.

The denominator is the part worth paying attention to. Divide by 100 and any ungraded category counts as a zero. Divide by the weights you actually entered and you get your standing on the work that has been graded. Those are different questions and they can be twenty points apart.

A syllabus with five categories. It is week ten, and the final exam has not happened:

Now the answer depends on which question you are asking:

• How am I doing so far? 66.35 ÷ 0.75 = 88.47%, a B+.
• What would I end with if nothing else were graded? 66.35 ÷ 1.00 = 66.35%, a D.

Same numbers, twenty-two points apart. The second is what many gradebooks display mid-term, and it is why a perfectly healthy course can look alarming in week ten. Neither figure is wrong — but only the first tells you how you are performing.

At the end of the term the ambiguity disappears, because the weights total 100%:

85.85%, a B. Note what the 78% on the final did: it was the lowest score in the course, and it pulled the grade down from the 88.47% standing above to 85.85% — a drop of more than two and a half points from a single assessment, because a quarter of the grade rode on it.

Courses use one of two systems, and confusing them is a common source of wrong answers.

Category weighting is what the examples above use: the syllabus assigns a percentage to each type of work, and how many assignments are in a category makes no difference to its share.

Points is the other system. Every assignment is worth points, and your grade is simply points earned over points possible:

680 ÷ 800 = 85%. A points system is still weighted — the final exam is worth 250 of the 800 available points, so it carries 31% of the grade — but the weighting is implicit in the point totals rather than stated as percentages.

To convert a points course into weights, divide each category's possible points by the course total. To go the other way, you cannot: weights tell you nothing about how many assignments produced them.

• Averaging the category averages. (95 + 88 + 82 + 91) ÷ 4 = 89, which ignores the weights entirely and happens to look close enough to be believed.
• Dividing by 100 when categories are ungraded. This counts them as zeros and produces the alarming mid-term number.
• Mixing points and percentages in one calculation. Convert a category to a percentage before applying its weight.
• Using the number of assignments as the weight. Ten homework assignments worth 20% together are worth 2% each, not 10% each.
• Forgetting a dropped score. If the lowest quiz is dropped, the quiz average must be computed without it before the weight is applied.
• Rounding each category first. Round once at the end; rounding four categories separately can shift the result across a letter boundary.

• Curves and adjustments are applied by your instructor after the arithmetic and cannot be predicted.
• Some courses have hurdles — a minimum exam score to pass regardless of the overall average. That is a rule, not a weight, and no calculation will show it.
• Rounding policy varies. An 89.5% is an A− at some institutions and a B+ at others.
• The syllabus is the authority. Where a gradebook and a syllabus disagree, ask your instructor rather than picking the one you prefer.