Use the grades you receive on all of your assignments for each individual category to calculate your total grade. For example, you had three homework assignments and scored 87 on each. You had two quizzes and scored a 100 and a 92. You had one exam, on which you scored 100. Add your homework scores together (87 + 87 +87 = 261). Add your quiz scores (100 + 92 = 192). Because you only have one exam you don't have to add that score.
Divide your total grade in each category by the number of assignments you had in that category. In this example, you will divide 261 by three for an average of 87 points on your homework grades. Divide 192 by two for an average of 96 on your quiz grades. Because you only had one exam, your exam average is 100 in this example.
Multiply the average score from each category by the percentage that category is worth. Multiply your homework score of 87 by 20 percent for a total of 17.4, your quiz grade of 96 by 30 percent for a total of 28.8 and your exam grade of 100 by 50 percent for a total of 50.
Add your final percentage from each category together to calculate your final grade. Add 17.4 to 28.8 to 50 for a total final grade of 96.2.