The short version
You need three numbers: your current grade, the grade you want, and how much the final is worth. Everything before the final counts for the rest of the class. Multiply your current grade by that share and you know how many points are already locked in. The final has to supply the gap.
That's one subtraction and one division. The hard part is getting the three inputs right, and that's where most students go wrong.
Formula notes
Needed on final = (target - current x (1 - final weight)) / final weight
A worked example
Say you have an 80% and the final is worth 40%. Your earlier work counts for 60% of the class, so it locks in 80 x 0.60 = 48 points. For an 85 in the course you need 37 more points from the final. Divide by 0.40 and you need 92.5% on the exam.
Now run the same class for other targets. For a 90 you'd need 105%, which means it's out of reach without extra credit. For an 80 you need exactly 80%, which makes sense: matching your current grade keeps it where it is. For a 70 you need 55%.
- Target 90: need 105% (not possible without extra credit)
- Target 85: need 92.5%
- Target 80: need 80%
- Target 70: need 55%
Why the final's weight changes everything
A heavy final can rescue a grade or sink it. With a final worth 25%, each 10 points on the exam moves your course grade by 2.5 points. With a final worth 40%, each 10 points moves it by 4. With 50%, it's 5.
This cuts both ways. If you're sitting at 86% and the final is worth 25%, a perfect exam only gets you to 89.5%, and a zero drops you to 64.5%. Knowing that range before you study tells you how much is at stake.
Three mistakes that give the wrong answer
First, copying a current grade that already counts the final as a zero. Some gradebooks do this, and it makes your current grade look much worse than it is. You want the grade on finished work only.
Second, using the wrong weight. If the final sits inside an Exams category worth 50% alongside two midterms, the final itself isn't worth 50%. Read the syllabus for the final's own share of the course.
Third, forgetting work that isn't graded yet. If a project worth 15% is still out, your current grade doesn't cover 100% minus the final. In that case, list every graded item with its weight and let the remaining weight stand for both the project and the exam.
When the answer is over 100% or under 0%
A result above 100% means the target can't be reached on a normal scale. Your options are extra credit, a curve, or a lower target. Don't count on a curve that hasn't been announced.
A result below 0% is good news. It means you'd reach the target even with a zero on the final. You still need to sit the exam if your class requires it, and some courses set a minimum exam score to pass, so check the syllabus.
Run your own numbers
Our weighted grade calculator has a final exam target mode that does this math. It also shows the best and worst grade you can still finish with, plus the course grade for exam scores from 0 to 100. If your class uses points instead of percentages, use the points mode and enter the final's possible points as the remaining work.
Once you have the number, treat it as a plan. Your instructor's gradebook, rounding and letter cutoffs decide the grade on your transcript.
Frequently asked questions
Is it possible to pass if I fail the final?
Often, yes, if your current grade is strong and the final isn't weighted heavily. Set your target to the passing grade and see whether the score needed is below 60%, or whatever counts as failing in your class.
What if my final is worth points instead of a percentage?
Divide the final's possible points by the total possible points for the course to get its weight. A 200-point final in a 1,000-point class is worth 20%.
Do I use my letter grade or percentage?
Use the exact percentage. A B could mean anything from 80% to 89.99%, and that spread changes the score you need by a lot on a heavy final.
Does rounding help me reach my target?
Sometimes. If your instructor rounds 89.5% up to 90%, you can aim for 89.5 instead. Check the syllabus, because many instructors don't round at all.
References
These sources support the method or guidance used for Grade Calculator. Verify time-sensitive rules at the source.
Try the calculator
Open Grade Calculator, enter your scenario, and compare its supporting rows with this guide's method and checks.