If a report card has ever puzzled you — two B quarters somehow becoming a different semester grade — the answer is almost certainly a weighting split. The most common is 40/40/20, and once you see the arithmetic, semester grades stop being mysterious.
The 40/40/20 split
Under this scheme:
- Quarter 1 counts 40% of the semester grade
- Quarter 2 counts 40%
- The final exam counts 20%
Semester grade = Q1 × 0.4 + Q2 × 0.4 + Final × 0.2.
A student with Q1 = 80, Q2 = 90 and a final of 100 finishes on 32 + 36 + 20 = 88 — a stronger result than either quarter alone would suggest, because the exam rewarded them at double weight relative to its raw share of the term.
Before the final: grade so far
Mid-semester, there is no exam score yet. The grade so far renormalises the two quarters: (Q1 × 40 + Q2 × 40) ÷ 80, which is simply their average — 85 for the student above. That is the number to watch in the portal; the final then pulls it up or down by up to 20% of its value.
Other splits you may meet
Schools also use 45/45/10 (exam worth less), 50/50 with no separate exam weighting, and six-weeks systems where three marking periods plus an exam combine differently. The structure is identical; only the weights change. Your school's handbook or the course syllabus states the split — it is a policy document, not a secret.
What the exam can and cannot do
Because the exam is "only" 20%, families sometimes underrate it. In truth a 20% component can move a semester grade by several points either way: from an 85 base, a perfect exam yields 88 and a disastrous 40 yields 76. It cannot rescue a failing year on its own — nor can one bad exam destroy a strong one. Both facts are worth knowing before exam week, not after.
Check your own semester
Enter your quarters and exam score — or work out the exam score you need — with the semester mode of the Weighted Grade Calculator and the Final Grade Calculator.