Almost every course calculates your final mark as a weighted average, which means some assignments matter far more than others. Once you understand the formula, you can work out your current grade at any point in the semester and calculate exactly what you need on the final exam to reach your target.

The Weighted Average Formula

A weighted grade is the sum of each score multiplied by its weight. If the weights add up to 100%, the formula is simply: weighted grade = (score 1 × weight 1) + (score 2 × weight 2) + and so on. For example, a course might count homework at 20%, quizzes at 15%, a midterm at 25%, a project at 15% and the final exam at 25%.

A Worked Example

Suppose you have scored 92% on homework, 85% on quizzes, 78% on the midterm and 90% on the project. The final has not happened yet. Your points so far are 0.20 × 92 = 18.4, plus 0.15 × 85 = 12.75, plus 0.25 × 78 = 19.5, plus 0.15 × 90 = 13.5, for a total of 64.15 points out of the 75 points that have been assessed.

Your current standing is therefore 64.15 ÷ 0.75 = 85.5%. This is a different number from 64.15%, which is only your running total toward a full 100 points. Many students panic when they see the smaller figure, so it is worth being clear about which one you are looking at.

How Much Do You Need on the Final?

Rearrange the formula to solve for the missing score: score needed = (target grade − points earned so far) ÷ weight of the final. With 64.15 points earned and a final worth 25%:

  • To finish with 80%, you need (80 − 64.15) ÷ 0.25 = 63.4% on the final.
  • To finish with 85%, you need (85 − 64.15) ÷ 0.25 = 83.4%.
  • To finish with 90%, you need (90 − 64.15) ÷ 0.25 = 103.4%, which is impossible without extra credit.

That last result is useful, not discouraging: it tells you early that a 90 is out of reach and lets you set a realistic goal instead.

Which Assignments Deserve Your Effort?

The impact of any improvement equals the weight multiplied by the points you gain. Raising your final exam score by 10 points adds 0.25 × 10 = 2.5 points to your course grade, while raising a 15% quiz category by the same amount adds only 1.5. When time is limited, put the most effort into heavily weighted components that you can still influence.

Points-Based Courses

Some courses skip percentages and simply total points: for example, 850 points earned out of 1,000. In that case, divide points earned by points possible so far, and compute what you need as points rather than percentages. The two methods give the same result as long as the weights are proportional to the points.

Common Mistakes

  • Averaging category scores without weights. A simple average of 92, 85, 78 and 90 gives 86.25%, not 85.5%, because the categories are not worth the same.
  • Forgetting that dropped scores change the maths. If the lowest quiz is dropped, remove it before averaging that category.
  • Treating curved or rounded grades as exact. Instructors may round up, curve the whole class or scale the final, and these policies are in the syllabus.
  • Using weights that do not total 100%. If they add up to something else, divide by the total of the weights you have used.

Letter Grades

Percentage-to-letter conversions vary: a common scale is A at 90 and above, B at 80 to 89, C at 70 to 79, and D at 60 to 69, but many institutions use different cut-offs, plus and minus grades, or relative grading. Always check your own syllabus.

Do this before the final

Write down every category, its weight and your score, work out your current standing, then solve for the final exam score you need. If the answer is above 100%, aim for the next grade boundary instead.