What grade do I need on my final exam?

The formula, and how to read it

Every weighted course splits into two pieces: the final exam, and everything else. The formula isolates the final. Take your target overall grade, subtract what your current grade already contributes (your current grade multiplied by the portion of the course that isn't the final), then divide by the final's weight.

Written out: grade needed = (target − current × (1 − final weight)) ÷ final weight. Weights go in as decimals, so a final worth 30% is 0.30, and the rest of the course is 1 − 0.30 = 0.70.

The key idea is that your existing grade is already "banked" at a fixed fraction of the total. The final only has as much power to move your average as its weight allows.

A worked example

Suppose you're sitting at 88% going into finals, the final exam counts for 30% of the course, and you want to finish with a 90%.

Plug it in: (90 − 88 × 0.70) ÷ 0.30. That's (90 − 61.6) ÷ 0.30 = 28.4 ÷ 0.30 = 94.7%. So you'd need roughly a 95% on the final to nudge an 88% up to a 90% overall.

Notice how much work the final has to do. Because it's only 30% of the grade, a two-point gain in your overall average (from 88 to 90) demands a score far above your current standing. The lighter the final's weight, the more extreme the required score becomes.

What moves the number, and when a target is out of reach

Three things drive the required score: how far your target sits above your current grade, the final's weight, and how much of the course is already locked in. A heavier final gives you more room to climb; a lighter one means each point of overall improvement costs more on exam day.

Two results are worth watching for. If the formula returns a number above 100%, the target simply isn't reachable with the final alone — no perfect score would get you there. If it returns something very low or negative, your target is already secured no matter how the final goes. You can test any combination of grades and weights on the Final Grade Calculator to see where your own cutoffs land.

Make the weights match your syllabus

The formula is only as accurate as the weight you feed it. The single most common error is guessing the final's weight instead of reading it off the syllabus. If your syllabus says the final is 25%, use 0.25 — not a rounded-off 0.30.

Courses also vary in structure. Some drop your lowest quiz, some add extra-credit points, and some weight categories (homework, midterms, participation) that then roll up into the non-final portion. When that's the case, your "current grade" should already reflect those rules before it enters the formula. Get the weights right and the arithmetic takes care of itself.