How do I work out what I need on the final exam?
Rearrange the weighted-average formula for the unknown. If the final is worth W percent of the course, your current grade is C over the remaining (100 minus W) percent, and you want an overall grade of G, then the score you need is (G minus C times (100 minus W) ÷ 100) ÷ (W ÷ 100). This calculator does that for each target grade so you can see all the thresholds at once.
What if the number I need is above 100?
Then the target is not reachable through the final alone, and it is better to know that early than to discover it afterwards. Your options are extra credit if offered, a resit or replacement policy, or accepting a lower grade. Some courses replace a low mid-term with a strong final, which changes the arithmetic entirely — worth asking about before assuming.
What if I need a very low score, or none at all?
If the required score is at or below zero, your target is already secured mathematically even with a zero on the final — though most courses require sitting the exam to pass regardless, and many have a minimum final-exam threshold independent of the average. Check for that rule before relying on the arithmetic.
How much does the final's weight change things?
Enormously, and it is the single most important input. A final worth 20% can only move your overall grade by a limited amount: even a perfect score lifts a 70% standing to about 76%. A final worth 50% can swing the outcome by twenty points or more. This is why students with a heavily weighted final should be told their standing well before the exam.
Does the calculation change for pass/fail or credit/no-credit courses?
The arithmetic is identical, but the target is a single threshold rather than a set of letter grades — often 60% or 70% for a pass. Be aware that some institutions require a higher percentage to pass a course taken pass/fail than the equivalent letter grade would need, and that pass/fail courses may not count toward GPA or major requirements.
Should I trust this over my instructor's figure?
No. Use it to plan, then confirm against the syllabus and your instructor. Real courses contain rules this cannot know: dropped lowest scores, curved grading, attendance components, late penalties, and minimum thresholds on individual assessments. The arithmetic here is exactly right for a simple weighted scheme, and simple weighted schemes are not universal.