What Do I Need on My Final? The Formula, Explained
The short answer
Score needed on the final = (grade you want − current grade × (1 − w)) ÷ w, where w is the final’s weight as a decimal. If you have an 88.5% going into a final worth 20% and want a 90% overall, you need (90 − 88.5 × 0.8) ÷ 0.2 = 96% on the final.
That one line covers most classes. The rest of this guide shows where it comes from, what to do when the answer is over 100% or below zero, and how to handle a class graded in points. The final grade calculator runs the same formula for every letter grade at once.
Where the formula comes from
Your grade after the final is a blend of two numbers:
- your grade before the final, which counts for everything except the final, and
- your score on the final, which counts for the final’s weight.
Overall = current × (1 − w) + final × w
You know every number except the final score, so solve for it:
- Subtract what you already have: target − current × (1 − w).
- That is the number of percentage points the final must supply.
- The final supplies w of the grade, so divide by w.
Needed on final = (target − current × (1 − w)) ÷ w
The weight is usually printed in the syllabus. A final “worth 20%” means w = 0.20, and your current grade counts for the other 0.80.
Worked example, step by step
You have an 88.5% before the final. The final is 20% of the grade. You want at least 90%.
- What you have already counts for 80%: 88.5 × 0.8 = 70.8 points.
- The final has to supply the rest: 90 − 70.8 = 19.2 points.
- Those points come from 20% of the final: 19.2 ÷ 0.2 = 96%.
Run it for other targets with the same numbers:
| Target | Calculation | Needed on the final |
|---|---|---|
| 93% (A on a plus/minus scale) | (93 − 70.8) ÷ 0.2 | 111%: out of reach |
| 90% (A−) | (90 − 70.8) ÷ 0.2 | 96% |
| 87% (B+) | (87 − 70.8) ÷ 0.2 | 81% |
| 83% (B) | (83 − 70.8) ÷ 0.2 | 61% |
| 80% (B−) | (80 − 70.8) ÷ 0.2 | 46% |
It works the other way round too. Score 80% on the final and you finish at 70.8 + 0.2 × 80 = 86.8%.
Lookup table: score needed to finish with 90%
Rows are your grade before the final; columns are the final’s weight.
| Current grade | Final 10% | Final 20% | Final 25% | Final 30% | Final 40% |
|---|---|---|---|---|---|
| 80% | out of reach | out of reach | out of reach | out of reach | out of reach |
| 85% | out of reach | out of reach | out of reach | out of reach | 97.5% |
| 88% | out of reach | 98% | 96% | 94.7% | 93% |
| 90% | 90% | 90% | 90% | 90% | 90% |
| 92% | 72% | 82% | 84% | 85.3% | 87% |
| 95% | 45% | 70% | 75% | 78.3% | 82.5% |
Two patterns stand out. If you are below your target, a heavier final gives you a better chance, because it can pull your grade further. If you are above your target, a heavier final is the riskier one, because a bad day costs more.
Lookup table: score needed to finish with 80%
| Current grade | Final 10% | Final 20% | Final 25% | Final 30% | Final 40% |
|---|---|---|---|---|---|
| 75% | out of reach | 100% | 95% | 91.7% | 87.5% |
| 80% | 80% | 80% | 80% | 80% | 80% |
| 85% | 35% | 60% | 65% | 68.3% | 72.5% |
| 88% | 8% | 48% | 56% | 61.3% | 68% |
| 90% | locked in | 40% | 50% | 56.7% | 65% |
| 95% | locked in | 20% | 35% | 45% | 57.5% |
When the answer is over 100% or below 0%
Over 100%. The grade you want cannot be reached on the final alone. With an 85% and a final worth 20%, even a perfect 100 only gets you to 0.8 × 85 + 0.2 × 100 = 88%. Check whether the exam has bonus questions or your teacher offers extra credit; otherwise, set the target one step lower and see what that needs.
0% or below. The grade is already locked in. With a 95% and a final worth 10%, a zero still leaves you at 0.9 × 95 = 85.5%. You should still sit the exam: some classes have rules about missed finals or a minimum score to pass, and those are not in the formula.
Classes graded in points
If your syllabus lists points instead of percentages, turn the final into a weight first:
w = points the final is worth ÷ total points for the whole term, including the final
Say the term is worth 1,000 points, the final is 200 of them, and you have earned 720 of the 800 points so far.
- Your current grade is 720 ÷ 800 = 90%.
- The final’s weight is 200 ÷ 1,000 = 0.2.
- To finish with 900 points (90%), you need 900 − 720 = 180 of the final’s 200 points, which is 90%. The formula gives the same answer: (90 − 90 × 0.8) ÷ 0.2 = 90%.
Make sure your “current grade” is right
The formula is only as good as the grade you put in. Two common traps:
- The gradebook already counts the final as zero. Online gradebooks handle missing work differently. UW-Madison’s notes on Canvas explain that some weighted setups count ungraded assignments against the student’s total while others leave them out, so the grade shown mid-term can swing. If the final is sitting in the gradebook as a zero, the number you see is lower than your real standing.
- Your grade is weighted by category. If homework, quizzes and tests each count for a set share, work your current grade out from the categories first. The grade calculator does that from your scores, then you can carry the result into the final grade calculator.
Check your school’s cutoffs
The formula gives a percent. Which letter that percent earns depends on your school. The College Board’s BigFuture GPA guide shows one common chart with an A from 90 to 100, and notes that some schools do not use pluses and minuses and others have different grade cutoffs. The tables above use a plus/minus scale with an A from 93; change the cutoffs in the calculator to match your syllabus.
Rounding matters at the edges too. Needed scores here use exact cutoffs, so a 90% target means 90.0%. If your teacher rounds 89.5 up, you may need slightly less than shown.
Common mistakes
- Using the weight as a whole number. A 20% final is 0.2 in the formula, not 20.
- Adding instead of blending. A 90 on a 20% final does not add 90 points; it adds 0.2 × 90 = 18.
- Forgetting the final is part of the total. In a points class, divide by the term’s full points, including the final’s.
- Ignoring policies. Dropped scores, curves and minimum exam scores change the picture. Your syllabus wins over any formula.
Related tools
- Final grade calculator: the score needed for every letter, and what a given score would leave you with.
- Grade calculator: your current grade from weighted categories or total points.
- GPA calculator: what this term’s grades do to your semester and cumulative GPA.
- Sleep calculator: a bedtime that fits full sleep cycles before exam morning.