Most course grades are weighted averages, not simple averages. Your syllabus splits the grade into categories — homework, quizzes, tests, projects, a final exam — and gives each a percentage weight. For each category, take your average percentage score, multiply it by its weight, add those products together, and divide by the total weight (usually 100). The result is your overall percentage, which maps to a letter grade on the standard scale (90–92% = A−, 87–89% = B+, 83–86% = B, and so on).
If a category has not happened yet, such as a final exam still to come, this calculator handles what you have completed; to find the score you need on what remains, use the Final Grade Calculator, which solves the same weighted-average equation backwards. Entering only completed work here and renormalising over the weights entered shows your standing on the work done so far.
The main assumption is that the weights you enter match your syllabus. Teachers occasionally drop the lowest quiz or curve a test, and those adjustments will not show up in a straight weighted average — so treat the result as an accurate calculation from the published weights, and ask your teacher how drops or curves apply to you.