The formula
needed = (target − current × (1 − weight)) ÷ weight, with the weight as a decimal.
Example: your current grade is 84%, you want 90%, and the final is worth 25%. You need (90 − 84 × 0.75) ÷ 0.25 = (90 − 63) ÷ 0.25 = 108% — so an A isn't possible without extra credit, but a B (80%) only needs (80 − 63) ÷ 0.25 = 68%.
Tips
- Use the grade shown in your online gradebook as your current grade, as long as it already accounts for weighting.
- Check the syllabus for the final's weight — it's often between 15% and 40%.
- If the result is above 100%, ask about extra credit or retakes; if it's below 0%, your target is already secured.