Why a weighted average is not a plain average of scores#
Most courses do not treat every assignment as equal. A midterm worth 30% of the grade and a quiz worth 5% should not pull the average the same way. The correct current grade is Σ(score × weight) ÷ Σ(weight). If you score 90% on something worth 20% and 70% on something worth 80%, the weighted average is 74%, not the midpoint 80%. Calculators that ignore weights — or that assume every row is worth the same — produce a number that will not match your syllabus.
Weights do not have to sum to 100% yet#
Mid-semester you often only have a subset of graded work. This tool divides by the total weight you have entered, so a partial list still yields a meaningful current average of what is already graded. The output also shows total weight used so you can see how much of the course is still outstanding. When you later add the remaining categories (or use Final needed for the exam), the picture becomes complete.
What “what do I need on the final?” actually solves#
If your current grade is C, the final is worth W% of the course, and you want a desired overall grade D, the required final score R satisfies D = C × (1 − W/100) + R × (W/100). Solving for R tells you the minimum score on the final. When R is above 100%, the target is unreachable without extra credit or a curve. When R is zero or negative, your current grade already meets or exceeds the target even with a zero on the final.
Letter grades on the fixed US percentage scale#
Letter output uses a common US scale: A at 90% and above, B at 80–89%, C at 70–79%, D at 60–69%, and F below 60%. Many schools use plus/minus cutoffs, different thresholds, or curved distributions. Treat the letter here as a convenient reference against that standard scale; always defer to your syllabus or registrar for official cutoffs.