You added your categories up, multiplied each one by its weight, and got 82. The gradebook says 87. Before you email anyone in a panic: almost every time, neither calculation is wrong — the two of you are averaging different sets of numbers. The gradebook is normally leaving something out that you put in, or applying a syllabus rule to the scores before the weighted formula ever runs.
Check in this order, because it is roughly the order the difference hides in: what is being counted, how each category is averaged, what the syllabus does to the scores first, and only then rounding. Nine times out of ten the gap closes on the first or second check, and you will be able to say exactly which number moved.
Every scale, weight, and rule below is a typical example — your syllabus and your school's policy hold the numbers that actually count.
Is something in the course not graded yet?
This is the most common cause by a wide margin, and it produces the biggest gaps — often twenty points or more.
Most gradebooks show a current grade: your standing across the work that has been graded so far. When you calculate by hand, you almost certainly filled the ungraded rows with zeros without noticing, which produces a projected grade for a term in which you score nothing on everything remaining. Those two numbers answer different questions, and mid-semester they can be nowhere near each other.
Here is a typical course, mid-term, with the final exam still ahead:
| Category | Weight | Your average |
|---|---|---|
| Homework | 20% | 92% |
| Quizzes | 30% | 84% |
| Projects | 20% | 88% |
| Final exam | 30% | not taken |
Multiply out what has been graded:
- Homework: 92 × 0.20 = 18.4
- Quizzes: 84 × 0.30 = 25.2
- Projects: 88 × 0.20 = 17.6
- Total: 61.2 points
Treat the ungraded final as a zero and your course grade reads 61.2%. Terrifying, and meaningless — you have not sat the exam yet.
The gradebook does something different. It counts only the 70% of the course that exists so far, and re-scales to it:
61.2 ÷ 0.70 = 87.43%
The book says 87.4, your arithmetic says 61.2, and both are correct answers to different questions. If the gap you are staring at is enormous, start here. The mid-semester version of this calculation is walked through in weighted grades explained.
What to do: decide which question you want answered. For "where do I stand right now", drop the ungraded categories and divide by the weights that have actually happened. For "what will I finish with", put a realistic score in the empty rows rather than a zero.
Is the missing assignment a zero, a blank, or excused?
The same missing homework can be entered three ways, and each one produces a different course grade.
- A zero counts as a score of 0 and pulls the category average down hard.
- A blank is usually excluded entirely, as though the assignment did not exist for you.
- Excused is explicitly excluded, and it is the only one of the three you can rely on being deliberate.
A teacher who leaves blanks while marking and converts them to zeros at the deadline will show you a grade that quietly falls one afternoon with no new work returned. If your number dropped and nothing came back to you, this is very likely why.
What to do: find the missing item in the list. If the cell shows a dash or is empty rather than a 0, it is probably not counting yet — and your grade will change when it does.
How is your category average being calculated?
Here is a subtler one, and it catches careful students in particular. Most gradebooks do not average the percentages inside a category. They add up the points earned and divide by the points possible, which quietly gives the bigger assignments more say.
Three quizzes: 8 out of 10, 45 out of 50, and 18 out of 20.
- Averaging the percentages — what most people do by hand: (80 + 90 + 90) ÷ 3 = 86.67%
- Totalling the points — what most gradebooks do: (8 + 45 + 18) ÷ (10 + 50 + 20) = 71 ÷ 80 = 88.75%
Two points of difference from identical scores. In a category worth 30% of the course that is 2.08 × 0.30 ≈ 0.6 of a point on your final grade — small, but exactly the kind of small that sits between two letter grades. And the more uneven your assignment sizes are, the wider the gap gets: one weak score on a ten-point quiz barely registers under the points method and hurts noticeably under the percentage method.
Which behaviour your course uses is a structural decision your teacher made before term started, and both are defensible — points-based and weighted gradebooks sets out what each one is optimising for.
What to do: recalculate one category both ways. If the points method matches the gradebook, you have your answer, and you now know how to compute every other category correctly.
What does the syllabus do to the scores before the formula runs?
The weighted formula is universal. The inputs are your teacher's rules, and four of them change the numbers before any multiplication happens.
Dropped scores. If the lowest quiz is dropped, four quizzes of 62, 88, 91 and 79 do not average 80.0 — they average (88 + 91 + 79) ÷ 3 = 86.0. Six points, from one rule. Check whether the drop applies per category or once overall, and whether it has kicked in at all; many gradebooks only apply it once a minimum number of scores exists.
Extra credit. In a weighted book, bonus points move only the category they were entered into, scaled by that category's weight. Five points added to a homework average in a category worth 20% move your course grade by 5 × 0.20 = one point, not five.
Late penalties. The score you were told and the score in the book may differ by a deduction applied at entry. Compare the number written on your returned work with the number on screen.
Weights that do not total 100. If the listed categories add up to 95%, most platforms normalise by dividing by 0.95, so every weight is effectively multiplied by about 1.05. Your hand calculation, using the printed weights, will land slightly low. When a syllabus makes this hard to check, how to judge a grading scheme covers the fine print worth reading before the first assignment.
If the gap is less than a point, it is rounding
A gradebook showing one decimal place can be holding more behind it: an 89.5 on screen may be a stored 89.46. Meanwhile your own calculation probably rounded each category average to a whole number before weighting, adding a little error at every step.
What to do: redo the calculation carrying two decimal places the whole way, and round only at the end. If a fraction of a point genuinely sits between you and a letter grade, ask what the stored value is and where the cutoff falls — that is a question about method, not a favour.
The ten-minute check that finds it
Work down this list and stop at the first mismatch.
- Write down the weights exactly as the syllabus lists them, and add them up. Do they total 100?
- List every category that has a graded score in it. Cross out the ones still empty.
- Recompute one category by totalling points, not by averaging percentages.
- Apply the syllabus rules — drops, extra credit, penalties — before you multiply anything.
- Multiply and add using only the categories that have scores, then divide by those weights.
- Compare. Still off by more than a point? Go back to step 2: an item you believe is graded probably is not.
What to ask your teacher
If you have done the check and the numbers still disagree, the email that gets answered fastest is short, specific, and asks about the method rather than the mark:
"I calculated my course grade as 82.4 using the weights in the syllabus, but the gradebook shows 87.4. Could you tell me whether the displayed grade includes the categories that haven't been graded yet, and whether category averages are calculated on total points? I'd like to be able to check my own standing correctly."
That is a question about how the system works, and it is easy to answer. "My grade is wrong" is an accusation, and it is not.
FAQ
Why did my grade drop overnight when nothing new was graded?
Almost always a missing assignment converted from a blank to a zero, or a late penalty applied at entry. Look for an item whose empty cell is now a 0.
Why does my grade swing up and down every week?
Early in a term each new score is a large share of a small pool, so single assignments move the average hard. The same score in week twelve barely shifts it. That volatility is arithmetic, not a system fault.
Does the gradebook's number or my calculation go on my report card?
The gradebook's, calculated under your school's policy. Your hand calculation is for understanding and planning — which is exactly why it is worth being able to reproduce the book's number.
My teacher's total and mine differ by half a point. Is it worth raising?
Only if it sits across a letter boundary. If it does, ask what the unrounded stored value is and where the cutoff falls, before assuming either number is wrong.
Can I check my grade if the gradebook only shows letters?
Yes, but you need the percentage bands first. Ask for the scale in writing, convert each letter to the middle of its band as an estimate, and treat the result as approximate until real percentages appear.
Rebuild it once, and it stops surprising you
A gradebook that disagrees with you is not usually a mistake. It is a different set of assumptions, and once you can name which one it is making, the number stops being frightening. Check what is counted, then how it is averaged, then what the syllabus does to the inputs. Rounding comes last — it is almost never the answer.
When you want to test a scenario rather than argue with one, use the free weighted grade calculator at addthismarks.com: one row per category, leave the ungraded ones out, and watch your standing update as you change a single score. Free, in-browser, no sign-up.
