How to Use This Tool
The question is always the same: what do I need on the final? The arithmetic is short, but the answer that matters most is the one many calculators refuse to give — that the target is out of reach and you should aim somewhere else.
The formula
Your final grade is a weighted average of what you have already earned and what the exam will earn. If
the exam is worth w as a decimal, then:
needed = (target − current × (1 − w)) ÷ w
With 78% banked, a final worth 30%, and a target of 85%: your existing work contributes 0.7 × 78 = 54.6 points, the exam must supply 85 − 54.6 = 30.4 points, and to produce 30.4 points from a 30% slice you would need 30.4 ÷ 0.3 = 101.3%. Which is to say: no.
Why the weighting dominates
People consistently overestimate how much a final can move their grade. A final worth 20% can shift your overall mark by at most 20 points in either direction, and only by going from zero to full marks. If your current grade is 78% and the final is worth 20%, every possible outcome lies between 62.4% and 82.4%. Nothing you do in that room puts an A in reach.
Reading the chart
The chart maps every possible exam score to the overall grade it produces. It is a straight line, and its steepness is the exam weighting. A flat line means the exam barely matters; a steep one means it decides everything. The table beneath lists the usual grade boundaries and marks which are still reachable, which is usually more useful than one number for one target.
Two things this cannot know
It assumes your current grade is a correct weighted average of everything marked so far, and that the remaining weight is entirely the final. If there is still coursework outstanding, or if the lowest score gets dropped, or if the course is curved, the answer here will be wrong. Curves in particular are unpredictable by design, and no calculator should pretend otherwise.
Also: percentages above 100 are shown rather than hidden. If you need 104%, that is the fact worth having early, so you can redirect the effort to a subject where it still changes something.
