One class might weight homework 20%, tests 50%, and the final 30%. Another might split it evenly three ways. A calculator that just averages every score you enter can't represent either syllabus correctly — it needs to know the actual weights.
Weighted grade calculator, your categories
Add as many categories as your class actually has — homework, quizzes, tests, participation, a final — with each one's weight percent and your score percent in it.
How to calculate my grade, without weights adding to exactly 100
Entered weights don't need to sum to precisely 100 — the calculator normalizes by whatever total you've entered, so a still-incomplete list of categories produces a correct proportional result.
Final grade calculator, work backward from a target
Add a "Final exam" category with its real weight, then try different score values in it until the overall grade hits the target you're aiming for.
