How this calculator works
Your course grade is already partly decided. Whatever percentage the final exam is worth — call it w — the rest of your work is locked at 1 − w and cannot change. A final worth 25% means 75% of your grade is fixed the moment you walk into the exam room.
So the calculator does not average your current grade with your final. It works out how much of your target is already covered by the fixed portion, then asks the final to cover the rest. That is why the required score is sometimes lower than your current grade (you are already above the bar and have room to drop) and sometimes above 100 (the bar is out of reach).
The formula
With w as the final’s weight expressed as a decimal — 20% becomes 0.20 — the three numbers on this page are:
best case = current × (1 − w) + 100 × w
worst case = current × (1 − w)
The required score is rounded up to two decimal places. That is deliberate: reporting 87.4% when the true requirement is 87.42% would tell you that you are safe at a score that leaves you short.
A worked example
You have an 88% going in. The final is worth 20% of the course grade. You want to finish with a 90% — an A- on a plus/minus scale.
already decided = 88 × (1 − 0.20) = 88 × 0.80 = 70.4
required = (90 − 70.4) ÷ 0.20
required = 19.6 ÷ 0.20 = 98
You need a 98% on the final. That is a hard number to hear, and it is exactly why the second half of the answer matters: a perfect final gets you to 90.4%, and a zero still leaves you at 70.4%. Your entire outcome range is 70.4 to 90.4. The A- is technically live but only barely; a B+ (87%) needs just 83% on the exam, which is a completely different evening of studying.
That is what the scenario table above the fold is for. One number tells you whether you hit your target. Ten numbers tell you what your semester actually looks like.
Letter grade cutoffs
Two scales are built in, and you can switch between them above. On the plus/minus scale an A starts at 93, A- at 90, B+ at 87, B at 83, B- at 80, C+ at 77, C at 73, C- at 70, D+ at 67, D at 63, D- at 60, and anything below 60 is an F. On the straight-letter scale it is 90 / 80 / 70 / 60. Pick the one your school uses — the difference between them changes the required score by several points.
Cutoffs vary more than students expect. Some instructors round 89.5 up to an A-, others truncate, and a few publish an explicit no-rounding policy. If your target sits within half a point of a boundary, that policy is worth finding before you build a plan around it.
When the number is bad news
Over 100%. The grade is gone. Drop your target by one letter and recalculate — the next letter down is frequently well within reach, and finding that out now is worth more than finding it out after the exam. It also frees the hours you were going to spend on an impossible target for a class where they still convert into grade.
Zero or below. Your grade is locked in and the final cannot take it from you. Check the syllabus for a minimum-final-score requirement, then spend the weekend on something that can still move.
Before you trust the number
Three things break the arithmetic, and all three are in your syllabus. First, a minimum score on the final required to pass the course — a rule that overrides everything else. Second, dropped lowest scores, which mean the current grade shown in your gradebook is pessimistic until the end of term. Third, conditional weighting, such as a final that replaces a lower midterm. Work out which rules apply to you, then run the numbers with those weights.
If your class is graded in raw points rather than percentages, the points-based calculator handles it without any conversion. If you need to work out your current grade from category averages first, start with the weighted grade calculator.