The formula
Let the current weighted average be C, the remaining work be worth w percent, and the target be T. Working in percentage points:
needed = (T × 100 − C × (100 − w)) ÷ w
Two other figures fall out of the same arithmetic and are usually more informative than the first:
Best achievable = (C × (100 − w) + 100 × w) ÷ 100
Already locked in = C × (100 − w) ÷ 100
Worked example, reachable
Current average 84.65%, final worth 25%, target 90%.
needed = (90 × 100 − 84.65 × 75) ÷ 25 = (9,000 − 6,348.75) ÷ 25 = 106.05.
That is above 100, so let us check the best case: (84.65 × 75 + 100 × 25) ÷ 100 = (6,348.75 + 2,500) ÷ 100 = 88.49%.
So the target is not achievable — a perfect final yields 88.49%. This is the single most valuable output of the calculation, and it is available weeks before the exam. Finding out that 90% is already out of reach changes how you approach the remaining components in a way that the raw number does not.
Worked example, reachable
Current average 84.65%, final worth 15%, target 88%.
needed = (8,800 − 84.65 × 85) ÷ 15 = (8,800 − 7,195.25) ÷ 15 = 1,604.75 ÷ 15 = 106.98% — still impossible. The locked-in figure is 84.65 × 0.85 = 71.95%, so the final carries 28.05 points of the 88 needed, over 15 points of weight.
Worked example that works: current 84.65%, final worth 25%, target 86%.
needed = (8,600 − 6,348.75) ÷ 25 = 2,251.25 ÷ 25 = 90.05%. Achievable, and the best case is 88.49% so there is genuine headroom. This calculator returns 90.05 rather than rounding, because on a borderline target the decimal matters.
Reading the locked-in number
The completed work contributes C × (100 − w) ÷ 100 to the final grade and cannot be changed. If that figure is already below the target by more than the maximum the remaining work can add, the target is gone. Conversely, if it is already at or above the target, the remaining work cannot drag the grade below it — which is the "already secured" case the calculator reports separately.
This is worth checking for one specific reason: a single low final cannot take a strong term below the pass threshold, because the earlier work is already counted. Students who believe one exam decides their grade are usually wrong in their own favour, and the arithmetic here shows by how much.
Where the conversion to GPA bites
Course percentage and GPA points are not linearly related, which means a small percentage target can be worth a large GPA jump or none at all. On a common 4.0 scale, moving from 86% to 90% crosses the A− threshold and moves 3.3 → 3.7, while moving from 80% to 82% stays at 2.7. The calculator shows the GPA points for your target and for a perfect final so you can see whether a stretch is worth the effort in transcript terms.
Three things that break the arithmetic
- A curve applied afterwards. If the course curves, the target percentage is not the target grade. Projections made before the curve are optimistic by an unknown amount.
- Dropping a component. If the lowest exam is dropped, the weights change and the current average must be recomputed over the remaining work — the inputs here would be wrong.
- Extra credit. Extra credit usually does not raise the denominator, so it can push a grade above 100 and change the letter grade non-linearly.
For the general treatment of weighting and curves, see the GPA and weighted grades guide.
Frequently asked questions
How do I find the final exam score I need?
Use needed = (target × 100 − current × (100 − weight)) ÷ weight. If the result is above 100, the target is not achievable; the calculator shows the best possible outcome in that case.
What if the required score is above 100?
Then the target cannot be reached even with a perfect final. The calculator reports this explicitly and gives the best achievable grade, so you can see the gap and decide whether it is worth pursuing the remaining components.
Can the final exam lower my grade below passing?
It depends on the completed work. The locked-in figure — current average × (100 − final weight) ÷ 100 — is already in the grade and cannot be removed, so a single low final usually cannot take you below a threshold that the earlier work already met.
Does this account for a curve?
No. The calculation works in raw percentages. If your course curves, the percentage target is not the grade target, and the final grade calculator should be re-run with the post-curve thresholds once they are published.