Your grade so far, worked through
Many syllabi split the grade into categories with a weight each. Say the split is homework 20%, quizzes 30%, midterm 25%, final 25%, and your scores so far are homework 92, quizzes 85, midterm 78, with the final still to come:
20 × 92 = 1840 · 30 × 85 = 2550 · 25 × 78 = 1950
6340 ÷ 75 (the weight graded so far) = 84.53%
The mistake to avoid is dividing by 100 instead of 75. That gives 63.40% — which is really the grade you'd finish with if you scored zero on the final, not the grade you have now.
What you need on what's left
Leave the final's score blank and type the grade you want. For 85% overall you need 86.40% on it. The result also shows the range you're working in: a perfect final brings you to 88.40%, a zero leaves you at 63.40%. So a target of 90% would need 106.40% — the calculator says that isn't reachable and shows 88.40% as the best you can do, rather than a score you can't get.
Extra credit
Teachers handle extra credit in different ways — added to the course total, to a single category, or as points on an assignment — and the syllabus or your teacher can tell you which. The Extra credit box adds percentage points to the course grade: 2 points takes 84.53% to 86.53%, and the final you need for 85% drops from 86.40% to 78.40%. If your extra credit goes into one category, add it to that category's score instead; the effect is smaller because it's scaled by the category's weight.
Points mode
Some classes skip categories and grade by total points. Switch to Points and enter earned and possible for each assignment. With 45/50 on the homework, 38/40 on the quiz, 82/100 on the test and a 150-point final to come, you have 165 of 190 = 86.84%.
For 90% overall you need 90% of all 340 points, which leaves 141 of the 150 on the final — 94.00%. Here extra credit is counted in points: 5 extra points lower that to 90.67%. On a smaller scale, 430/500 plus 10 extra-credit points is 88.00%.
Points and weights can give different answers for the same scores, because in points mode a 150-point final counts 3 times as much as a 50-point homework set. Use whichever your syllabus describes.
Questions
How do I calculate a weighted grade?
Multiply each category's score by its weight, add them up, and divide by the total weight of the categories that have been graded. With homework 20% at 92, quizzes 30% at 85, midterm 25% at 78, that's 6340 ÷ 75 = 84.53%.
What if my syllabus weights don't add up to 100%?
The calculator divides by whatever the weights add up to, so it still gives an answer, and it shows the total so you can spot a typo. If your total is over 100%, check the syllabus — a category may have been entered twice.
How does extra credit affect my grade?
It depends on how your teacher adds it. Here, extra credit in weights mode is added straight to the course grade (2 points turns 84.53% into 86.53%); in points mode it's added to the points you earned. If your teacher adds it to one category instead, put it into that category's score.
Should I use weights or points?
Whichever your syllabus uses. If it lists categories with percentages, use weights. If every assignment is worth a number of points and your grade is total earned over total possible, use points — big assignments then count for more automatically.
What grade do I need on the rest of the class?
Leave a score blank for anything not graded yet and type the grade you want. With the final (25%) still to come, finishing at 85% takes 86.40% on it. If it's only the final that's left, the final grade calculator is quicker.