Enter each graded item with its score and its weight to see where you stand. Then name a target grade and the calculator works out what the remaining work has to score — and tells you plainly when that number is above 100 and the target is no longer reachable.
Subtract the points you have already banked from your target, then divide by the weight of the final as a decimal. If you have 43.6 of a possible 100 and want 90, with the final worth 50%, you need (90 − 43.6) / 0.5 = 92.8%.
Two different questions. The overall figure counts ungraded work as zero, so it is low until everything is marked. The current average divides only by the weight graded so far, which is the honest picture of how you are doing. Both are shown.
Then that grade is out of reach with the weighting as entered, and the calculator says so along with the highest grade still possible. Worth checking whether extra credit, a dropped lowest score or a curve applies before concluding anything.