Every December and May, teachers get the same question: "What do I need on the final to get a B?" The math takes about a minute, and it's worth showing students how to do it themselves.
The formula for weighted classes
If the final exam is worth a fixed percentage of the course grade:
Needed = (Target − Current × (1 − w)) ÷ w
where w is the final's weight as a decimal.
Example. A student has an 82% going into the final. The final is worth 20% of the course grade. They want an 85%.
Needed = (85 − 82 × 0.80) ÷ 0.20 = (85 − 65.6) ÷ 0.20 = 19.4 ÷ 0.20 = 97%.
Same student, but they'd be happy with an 80: (80 − 65.6) ÷ 0.20 = 72%.
That gap is the useful part. A five-point change in the goal moves the needed score by 25 points when the final is worth 20%. The smaller the final's weight, the more dramatic this gets.
The formula for points-based classes
If your course is a straight total of points, add the final to the denominator.
Example. A student has earned 820 out of 1,000 points. The final is worth 200 points. For 85% overall, they need 0.85 × 1,200 = 1,020 total points, so 1,020 − 820 = 200 points. That's a perfect final. For 80%, they need 960 − 820 = 140, or 70% on the final.
When the answer is over 100
If the formula says a student needs 112%, the target can't be reached with the final alone. That's not a failure of the math; it's the start of a planning conversation. Can they still make up missing work? Does your retake policy allow reassessing an earlier unit? If neither, helping them set a reachable goal is kinder than letting them cram for an impossible one.
When the answer is very low
A student who "needs a 34" may decide not to study. Worth a word: a bad enough final can still move a grade down, and in many schools the final also feeds into placement decisions. Run the formula for the grade below their current one, too, so they see what's at risk.
Make it routine
Post the formula in your LMS before finals week, with one worked example using your actual final weight. It cuts down on individual questions and helps students practice exactly the kind of proportional reasoning we'd like them to have anyway. For a refresher on how the course grade itself is built, see how to calculate weighted grades.