The score you need on the final
Here w is the final's weight as a decimal (a 20% final is 0.20), current is your grade going in, and goal is the overall grade you want. Everything except the final already counts for (1 − w) of your grade, so you only have to make up the gap through the slice the final controls.
What a perfect final can actually get you
A 100% final adds at most its own weight to your average. That sets a hard ceiling — if your target sits above it, no score saves you. This is why "needed" often comes out above 100%.
| Current grade | Final weight | Best possible overall |
|---|---|---|
| 85% | 10% | 86.5% |
| 85% | 20% | 88.0% |
| 85% | 30% | 89.5% |
| 75% | 30% | 82.5% |
| 70% | 50% | 85.0% |
Best possible = current × (1 − w) + 100 × w. If the grade you want is higher than this, aim for a realistic overall grade instead.
Two things people mix up
- Final grade vs final exam. Your final grade is the whole course average. The final exam is one component of it — usually the heaviest, but still just one weight in the mix.
- Check the real weight. 20% is common but far from universal; some syllabuses put the final at 30% or 40%. A few points of weight moves the answer a lot, so use the number on your own syllabus.
Common questions
What grade do I need on the final to pass?
Take the score you want, subtract what your current grade contributes, then divide by the final's weight. If you have an 85% going in, the final is worth 20%, and you want 90% overall, you need (90 minus 85 times 0.80) divided by 0.20, which is 110% — impossible. The most you could reach is 88%.
What if the answer is over 100%?
It means the grade you want is out of reach no matter how well you do on the final. A perfect final only adds its full weight, so with an 85% average and a 20% final, the ceiling is 85 times 0.80 plus 100 times 0.20 = 88%.
Does the final exam weight really change the math this much?
Yes. A heavier final gives your last score more pull. To move your overall grade up 10 points you need about 50 points above your current average on a 20% final, but only about 20 points above it on a 50% final.
