The formula
required = (target − current × completed weight) / final weight
Your overall grade is a weighted average: the part already graded, at its weight, plus the final exam at its weight. The formula simply solves that average for the one unknown, the final exam score. Weights go in as decimals and must sum to 1 across the whole course.
The worked case
Current grade 78%, with 60% of the course completed; target 80% overall; final worth the remaining 40%:
(80 − 78 × 0.6) / 0.4 = (80 − 46.8) / 0.4 = 83%
You need 83%, five points above your running average. That gap is the rule, not the exception: whenever your target exceeds your current grade, the final must outperform the target, because it is dragging the average up with only its own weight as leverage.
How the required score moves
Same 78% current grade and 80% target, at different final-exam weights:
| Final weight | Completed weight | Needed on final |
|---|---|---|
| 20% | 80% | 88% |
| 30% | 70% | 84.7% |
| 40% | 60% | 83% |
| 50% | 50% | 82% |
A heavier final is your friend when you are behind, more leverage to move the average, and your enemy when you are ahead, since it can equally drag a good grade down. The same table read in reverse tells a student at 85% aiming to keep an A− exactly how much cushion exists.
When the answer exceeds 100%
No reachable score gets you there. The honest responses, in order: check for policies that repair the completed portion (dropped quizzes, regrades, extra credit, these change current, which the final cannot); recompute with 100% as the final score to learn your best achievable grade; then aim at the highest target that is actually on the table. Knowing a goal is dead two weeks early is worth more than discovering it after the exam, it reallocates scarce study hours to courses where they still buy something.
Using it well
- Run it early. The formula works at any point in the term, after each midterm, the "required final score" is a live health metric for the course.
- Get the weights right. The output is only as good as the syllabus reading. Renormalise your current grade over completed weights only; mixing graded and ungraded weights is the classic error.
- Set two targets. The grade you want and the grade you need (a cutoff for a scholarship, a major requirement). Study to protect the second while pursuing the first.
The surrounding arithmetic lives nearby: the percentage calculator handles mark-to-percentage conversions when your gradebook reports points, the GPA calculator shows what the resulting course grade does to the credit-weighted bigger picture, and the days between dates calculator counts the study days you actually have left.