A worked example: 78% so far, final worth 30%, target 82%
With a 78% average so far and a final exam worth 30% of the overall grade, reaching an 82% overall target requires scoring 91.33% on the final.
The formula: rearranging overall = current×(1−weight) + final×weight
The standard weighted-average formula sets overall grade equal to the current average times its share of the weight, plus the final score times its own weight. Rearranging to solve for the unknown final score: (desired overall − current×(1−final weight)) ÷ final weight = (82 − 78×0.70) ÷ 0.30 = 91.33%.
When the target isn't achievable: 60% so far, needing 90% overall
A 60% current average with a final worth only 20%, targeting a 90% overall grade, computes to a required final score of 210% — impossible, since no score can exceed 100%. This means the 90% target isn't reachable at all given the current standing and the final's limited weight.
What a negative required score would mean
A calculated needed score below 0% means the opposite situation — the target overall grade is already secured regardless of the final exam result, since even a score of zero on the final wouldn't be enough to pull the overall average below the target.
Where the "current average" input actually comes from
This current average needs to reflect every graded component except the final — typically computed with a weighted-average calculation across just those non-final components, using their own relative weights rather than assuming they're all worth the same amount.