The score you need on your final depends on three numbers: your grade now, how much the final is worth, and the grade you want to finish with. Here is the formula and how to use it.
The formula
Needed on final = (goal − current × (1 − w)) ÷ w
w is the final’s weight as a decimal: 20% is 0.2 and 25% is 0.25. Your current grade covers the rest of the course, which is 1 − w.
Worked example
You have 84% in the class, the final is worth 20%, and you want at least 80%.
- The work already done is worth 80% of the course: 84 × 0.8 = 67.2 points.
- You need 80 − 67.2 = 12.8 more points.
- The final carries 20 points of the 100, so you need 12.8 ÷ 0.2 = 64% on it.
Check it: 67.2 + 0.2 × 64 = 80. The final grade calculator gives this for every letter grade at once.
How the final’s weight changes things
With 84% now, the score you need for an 80% course grade changes a lot with the final’s weight:
| Final’s weight | Needed for 80% | Needed for 90% |
|---|---|---|
| 10% | 44% | 144% (not possible) |
| 20% | 64% | 114% (not possible) |
| 25% | 68% | 108% (not possible) |
| 40% | 74% | 99% |
A heavily weighted final can rescue a grade, or sink one. With a light final, your grade is mostly decided already.
If the answer is over 100%
Then that grade can’t be reached through the final alone. Your best case is a perfect score: with 84% now and a final worth 20%, a 100% gives 67.2 + 20 = 87.2%. That’s still enough for a B+ on most scales.
If the answer is zero or below
You’ve already secured that grade. Even a zero on the final keeps you at current × (1 − w). With 84% and a 20% final, that’s 67.2%. Skipping the final is rarely a good idea, though: a zero still counts.
When the formula doesn’t fit
- More work still to be graded. If projects or homework are still coming, your current grade will change before the final. Work it out again once they’re in.
- Finals that replace a grade. Some teachers let the final replace your lowest test, or count it only if it helps. Then the usual formula doesn’t apply.
- Points instead of weights. If the class is points-based, the final’s weight is its points divided by the course’s total points. A 200-point final in a 1,000-point class is worth 20%.
Quick tips
- Use your grade before rounding, exactly as the gradebook shows it.
- Check the final’s weight in the syllabus, not from memory.
- Aim a few points above the number you need. Exams rarely go exactly to plan.