The formula behind the final grade calculator
Your final course grade is a weighted average of everything before the final and the final itself:
Final grade = current grade × (1 − w) + final exam score × w, where w is the final's weight as a decimal.
Solving for the exam score gives the number you actually want:
Score needed = (target − current × (1 − w)) ÷ w
Worked example
You have an 82% in the class, the final is worth 25%, and you want at least an 80% (a B). The score needed is (80 − 82 × 0.75) ÷ 0.25 = (80 − 61.5) ÷ 0.25 = 74%. If you want an A (90%), you would need (90 − 61.5) ÷ 0.25 = 114%, which is out of reach without extra credit.
Why the weight matters so much
When the final is worth 10%, it can only move your grade by a few points either way. When it is worth 40% or 50%, as in many college courses, a single exam can lift or sink the grade by a full letter. The table under the result shows the score needed for each letter grade, so you can set a realistic goal and plan your study time.
Weighted categories
Many syllabi split the grade into categories, for example homework 20%, quizzes 15%, tests 40% and the final 25%. Switch to the weighted tab, enter each category's average and weight, and the calculator works out your current grade first. If the weights you enter do not add up to 100, it rescales them, which is how most online gradebooks report a grade before every category has scores.
Tips
Frequently asked questions
How do I calculate what I need on my final?
Required final = (target grade − current grade × (1 − final weight)) ÷ final weight. With an 85% current grade, a 90% target and a final worth 20%, you need (90 − 85 × 0.8) ÷ 0.2 = 110%.
What does it mean if I need more than 100%?
It means the target cannot be reached with the final alone, unless extra credit is available. Look at the table to see the highest letter grade you can still reach.
How do I find my current grade with weighted categories?
Multiply each category average by its weight, add them up and divide by the total weight. Use the weighted categories tab to do this automatically.
What if my final replaces my lowest test?
Then the math changes; ask your teacher how the replacement works. You can model it by entering the new category averages in the weighted tab.
Does the calculator use a standard letter scale?
The table uses 90/80/70/60 cutoffs. If your school uses plus/minus grades or a different scale, enter the exact target percentage instead.
Sources and official references
- Weighted averages explained – Khan Academy
Last reviewed October 10, 2026. Results are estimates for planning; see our disclaimer.
