Two marking periods plus an exam. Enter your quarters and the split your school uses, and we work the semester grade — or the exam score you need for the one you want.
Your semester grade
a B on a 40 / 40 / 20 split
Letter gradeB
Split used40 / 40 / 20
Exam needed to hold it57%
Split
40 / 40 / 20
Marking periods
88% & 91%
Exam
76%
Semester grade
86.8% (B)
This calculator needs JavaScript to recalculate. The answer shown above was worked out when the page was built and is correct for the date in the address bar.
A semester grade is not the average of your two quarter grades. It is a weighted average of the two quarters plus a semester exam, and the weights are set by your district. The two you will meet most often are 40 / 40 / 20 and 45 / 45 / 10, and the difference between them decides how much damage a bad exam can do.
On a 40/40/20 split the exam can move your semester grade by up to 20 points. On 45/45/10 it can move it by 10. That is the whole story of whether the exam is worth losing sleep over, and it is written on your syllabus or your course outline.
Notice what the exam did. Without it, the quarters average 89.5. The 76 pulled the semester down 2.7 points and cost a letter grade at most schools. On a 45/45/10 split the same exam would have cost 1.35 points and left the B+ intact.
Working backwards
Say you want an 88 for the semester and the exam has not happened yet. Rearranged: exam = (88 − 35.2 − 36.4) ÷ 0.20 = 82%. That is the same shape of question the final grade calculator answers for a full course, and if what you actually need is "what do I need on my final", that page shows every letter grade at once.
The formula
S = q₁w₁ + q₂w₂ + eₓwₓ, with weights entered as decimals summing to 1. If your weights do not sum to 1 we normalise by their total, so a partial entry still gives a meaningful answer.
Reverse: eₓ = (S_target − q₁w₁ − q₂w₂) ÷ wₓ.
Where this stops being reliable
Some districts average the two quarters first and then apply the exam weight to that average, which is not the same calculation and gives a different answer when the quarters differ. Some allow exam exemptions for students above a threshold, in which case the semester grade is just the quarter average. Trimester systems have three marking periods rather than two and this model does not fit them. And some schools round the semester grade to a letter at each quarter before combining, which compounds rounding in ways no formula can reconstruct.
If your school's number and this one disagree by a point or so, the averaging order is the first thing to check.
Common questions
How is a semester grade calculated?
Each quarter and the semester exam get a fixed weight, most commonly 40 / 40 / 20 or 45 / 45 / 10. Multiply each score by its weight and add them together. Quarters of 88 and 91 with a 76 exam on a 40/40/20 split give 86.8%.
Can the semester exam drop my letter grade?
Yes, and on a 40/40/20 split it easily can — an exam 15 points below your quarter average costs about 3 points on the semester grade, which is enough to cross a boundary. On a 45/45/10 split the same exam costs about 1.5 points. Check which split your school uses before deciding how worried to be.
What happens if I am exempt from the exam?
Your semester grade becomes the weighted average of the two quarters alone, usually 50 / 50. Set the exam weight to zero above and the calculator handles it. Exemption rules are set by the school and typically require a minimum grade and an attendance threshold.
Where do I find my school's semester split?
Usually on the course syllabus, the student handbook, or the grading policy page of the district site. If the report card shows a semester grade alongside two quarters and an exam, you can also work the split out backwards from a past semester — enter your old numbers and try each preset until it matches.
Do semester grades or quarter grades go on my transcript?
At most US high schools the semester grade is what appears on the transcript and what counts toward GPA; quarter grades are progress reports. That varies by district, and a few record quarters as well, so check your handbook if it matters for a GPA calculation.
My school averages the quarters first, then applies the exam. Is that different?
Yes, whenever the two quarters are not equal. Averaging first treats both quarters as one block, which slightly changes the result compared with weighting them separately. If your school does it that way, average your quarters yourself and enter the result in both quarter fields.