The formula
If the final is worth w of your overall grade (as a decimal), the rest of the course counts for 1 − w. The score you need is:
Required final = (desired − current × (1 − w)) / w
For example, with a current grade of 85%, a final worth 20% and a goal of 80%: (80 − 85 × 0.8) / 0.2 = (80 − 68) / 0.2 = 60%.
Step by step
Say your current grade is 78%, the final is worth 25% and you want to finish with at least 80%:
- Turn the final's weight into a decimal: 25% = 0.25. The rest of the course counts for 1 − 0.25 = 0.75.
- Work out what your current grade contributes: 78 × 0.75 = 58.5 points.
- Subtract that from your goal: 80 − 58.5 = 21.5 points still needed.
- Divide by the final's weight: 21.5 ÷ 0.25 = 86%. That is the score you need on the final.
| Goal | Final score needed |
|---|---|
| 60% | 6% |
| 70% | 46% |
| 80% | 86% |
| 90% | 126% (not reachable) |
What different final scores would give you
Running the formula the other way shows your overall grade for a given exam score: overall = current × (1 − w) + final × w. With the same 78% and 25% weight:
| Final exam score | Overall grade |
|---|---|
| 0% | 58.5% |
| 60% | 73.5% |
| 70% | 76% |
| 80% | 78.5% |
| 90% | 81% |
| 100% | 83.5% |
Every 10 points on the final moves the overall grade by 2.5 points here, because 10 × 0.25 = 2.5. The heavier the final, the more it can move your grade in either direction.
Reading the result
- Over 100%: the goal can't be reached with the final alone, unless extra credit is available.
- 0% or less: you'll reach the goal even if you score 0 on the final.
- The table shows the overall grade you'd end up with for a few possible final scores.
If you are aiming for a letter grade, enter the lowest percentage for that letter in your syllabus as the goal. Ask your instructor whether final grades are rounded, since 89.5% counts as an A− in some classes and a B+ in others.