The one formula
Your course grade is the sum of each item's mark times its weight, divided by the total weight of everything graded so far. If you scored 80% on a 20% midterm and 70% on a 10% assignment, you have (80 × 20 + 70 × 10) ÷ 30 = 76.7% on the 30% of the course that's been marked.
The important half of that sentence is the denominator. Until the term is over, your standing is out of what's been graded, not out of 100.
What a mark is really worth
Multiply the mark difference by the weight. Going from 70 to 90 on a 5% quiz moves your final grade by 20 × 0.05 = 1 mark. The same improvement on a 35% final moves it by 7.
This is why studying for the thing in front of you is often the wrong call. The correct question is always “how many final-grade points is this hour worth”.
Working out what you need on the final
Take the grade you want, subtract what you've already banked (each mark times its weight, as a share of 100), then divide by the final's weight.
Example: you want 80 overall. You've earned 48 marks out of the 60% graded so far. The final is worth 40%. You need (80 − 48) ÷ 0.40 = 80% on the final.
If that number comes out above 100, the grade you want is no longer available, and it's better to know in week 10 than in the exam room.
Traps in real outlines
- Weights that don't sum to 100. It happens. Ask before the first test, not after the last.
- “Best 3 of 4 quizzes”. Your effective weight per quiz changes depending on which you drop.
- A hurdle: some courses require a minimum on the final exam to pass regardless of your other marks. This is in the outline and almost nobody reads it.
- Bonus marks that are capped, or applied before rather than after rounding.
- Participation marked at the professor's discretion, which is not something you can calculate around.
Do it without the arithmetic
The free final grade calculator does the “what do I need on the final” version in one screen. SyllaBuddy does the running version: enter marks as you get them and it keeps your standing per course up to date, using the weights it pulled from your outline, and will tell you when a target has gone out of reach.
Questions
Does a 0 on a small assignment really matter?
A zero on a 5% item costs 5 final marks, which is often a full letter grade band. The weight is small; the zero is not.
How do I calculate my grade if some things aren't marked yet?
Divide by the weight of what has been marked. That gives your current standing. Treating unmarked work as zero gives you a number that means nothing and feels terrible.