The two numbers a weighted gradebook can produce
Weighted grading multiplies each category percentage by its weight, adds the products, and divides. The division is where the ambiguity sits. If homework at 20, quizzes at 15, labs at 10, the midterm at 20, projects at 15 and the final at 20 have all been graded, the weights total 100 and there is only one answer. Take the final exam out because it has not happened yet and the graded weight is 80, and now the software has to decide whether to divide by 80 or by 100.
Dividing by 80 rescales: it reports what the grade would be if the term ended now and the ungraded work simply did not exist. Dividing by 100 treats the missing 20 as twenty points of nothing, which drags the reported figure down by roughly a fifth. Both behaviours exist in real gradebook software, sometimes as a setting nobody remembers changing. This page shows both, side by side, rather than picking one, because the choice is not arithmetic — it is a setting and a policy, and the policy is your school's.
The same fork appears when the weights themselves do not total 100. Weights of 20, 15, 10, 20, 15 and 15 add to 95. Rescaling divides by 95 and gives a defensible grade. Taking them literally divides by 100 and quietly subtracts about four points from a student sitting in the mid eighties. That is the failure worth catching in week two rather than week eighteen, and it usually happens because a category was split in half or dropped and the rest were never adjusted.
The unweighted mean is not the grade
Averaging the six category percentages as if they were six equal numbers is the most common error in this whole area, and it is common precisely because it looks reasonable. A student at 86 in homework, 85.33 in quizzes, 94 in labs, 78 on the midterm, 88 in projects and 84 on the final has a plain mean of 85.89 and a weighted grade of exactly 85.00. Nine tenths of a point, and easy to shrug at.
The gap widens as fast as the weights diverge. Take four categories at 95 percent between them holding 60 percent of the weight, and a final worth the other 40 that the student scored 70 on. The plain mean of those five categories is 90. The weighted figure is 0.6 times 95 plus 0.4 times 70, which is 85. That is two bands apart on most scales. The tool prints both so the size of the gap is visible for the actual numbers in front of you rather than in the abstract.
Why the small category is the dangerous one
Intuition says a zero hurts most in the heaviest category. That is only half of it. What a zero changes is the category percentage, and a category percentage moves in proportion to how few points are already in it — so the damage is the weight multiplied by how big the zero is relative to the pile it lands on.
| Category | Weight | Points so far | Effect of one 20-point zero |
|---|---|---|---|
| Labs | 10% | 50 | Category falls about 27 points, course grade falls about 2.69 |
| Midterm | 20% | 100 | Category falls 13 points, course grade falls 2.60 |
| Homework | 20% | 200 | Category falls about 7.8 points, course grade falls about 1.56 |
The 10 percent lab category does slightly more damage than the 20 percent midterm, because it holds half as many points, and both do far more than the homework category on the same weight. Enter your own figures above and the table in the results does this for every category at once. It is the single most useful thing to look at when a category is set up thinly — a handful of points carrying a real weight is a fragile arrangement, and it is fragile for the strongest students as much as the weakest.
What this page will not do
It will not tell you what the weights should be, what counts as a passing grade, whether late work should be accepted, or whether a zero should be entered at all rather than left blank. Those are set by the district, the school, the department and sometimes by state law, and they differ enough that any default here would be wrong somewhere. Every threshold on this page is a field you fill in, including the letter scale.
It also holds no roster. There are no names, no identifiers and no saving of any kind — the calculation runs in your browser and nothing is transmitted or kept. Anything involving actual student records belongs in the system your school has approved for it.
For the student-facing version of this arithmetic — one course, and what the final exam has to score to reach a target — the test average calculator solves the same equation for the unknown instead. Across courses, the GPA calculator handles credit weighting, which behaves the same way one level up. If you are about to apply a curve to the result, the grade curve calculator shows what each method does to the class as a whole, and class rank places one score inside a distribution.
Questions people ask
Do the category weights have to add to 100?
Mathematically no, and that is exactly why the error survives. Any set of weights produces an answer as long as you divide by their total. The problem is that gradebook software does not always divide by their total — some configurations divide by 100 regardless, which turns a weight set of 95 into a penalty applied to everyone. The tool prints both readings so you can see the size of the discrepancy for your numbers. Which one your gradebook actually does is a question for whoever administers it, and the weights themselves should match the syllabus students were given.
Why does an ungraded category change the answer so much?
Because it is the same question as weights not summing to 100, arriving by a different route. A final exam worth 20 percent that has not been sat leaves only 80 percent of the weight graded. Rescaling divides by 80 and reports where the student stands on the work that exists. Dividing by 100 treats the unsat exam as a zero, which is not a statement about the student at all. Mid-term progress reports are where this bites, because a parent reading a figure that included an unsat final would be reading something meaningless. Check which behaviour your system uses before the reports go out.
Should a missing assignment be entered as a zero or left blank?
That is a policy question and this page does not answer it, because districts and schools take genuinely different positions and some of them are written into board policy. What the page does give you is the arithmetic cost, which is the input that policy discussion usually lacks. Enter the point value in the missed-assignment field and the results table shows what a zero does in each category — including the result most people find surprising, which is that a small category with few points in it can take more damage than a large one carrying more weight.
Can I use points-based grading instead of weights?
Total points grading is a different system: every assignment goes into one pool and the grade is total earned over total possible, with weight emerging from how many points each thing is worth. If that is what you run, put a single line in with a weight of 100 and your running totals, and the result is simply the percentage. The interesting comparison is entering the same class both ways, because a total points scheme silently weights by point value, and the weights it produces are rarely the ones a teacher would have chosen deliberately.
Does this store anything about my class?
No. There is no account, no upload and no saving — everything is computed in the page in your browser and vanishes when you close the tab. There is deliberately no field for student names, because a public web page is not the right place for anything identifying a student. Keep individual records in the system your school has approved, and use this for the structure of the gradebook rather than its contents. If you need a printable blank for the paper side of the same job, the attendance sheet maker builds one in the browser the same way.