A worked example: four components at 20/20/25/35% weight
Scores of 85, 78, 92, and 88, weighted at 20%, 20%, 25%, and 35% respectively, average to an overall 86.4% — a letter grade of B.
The formula: weighted sum, divided by total weight
Each score multiplies by its own weight; those products sum together, then divide by the sum of all the weights. Dividing by the total weight (rather than assuming weights sum to exactly 100) means relative weights like 2, 2, 3 work identically to percentages that add up to 100.
A course still missing its final: three components summing to 70% weight
Scores of 82, 75, and 88 at weights 25%, 25%, and 20% (summing to 70%, with the final exam's 30% still unaccounted for) average to 81.21% so far — a running average based only on the graded components entered.
Why a heavily-weighted component matters more
A component weighted at 35% moves the overall average roughly 3.5 times as much as an identical score change on a component weighted at only 10% — which is exactly why knowing the weights, not just the scores, is essential for understanding where a grade actually stands.
What this running average is useful for next
A current average based on everything graded except a remaining component — like a final exam — is exactly the figure needed to work out what score that remaining component requires to hit a target overall grade.