Your semester GPA is the credit-weighted average of all the grades you earn in a single academic term. Unlike a simple average of letter grades, it accounts for the fact that a 4-credit course should influence your GPA more than a 1-credit elective. Understanding the math makes it easier to plan strategically.
The 4.0 scale explained
Most American universities use a 4.0 scale where each letter grade maps to a numeric point value. A/A+ both earn 4.0, A− earns 3.7, B+ earns 3.3, B earns 3.0, and so on. F earns 0.0 and still consumes credit hours in the denominator — a failed course drags your GPA even if you retake it (unless your school has grade forgiveness policies). Multiply each grade's point value by the course's credit hours to get 'quality points,' sum all quality points, then divide by total credit hours. That's your semester GPA.
Why credit hours matter more than course count
A student taking a 4-credit lab science and earning a C will see a bigger dip in GPA than a student earning a C in a 2-credit elective. Credit hours are the weights in the weighted average. This is why engineering and pre-med students who carry heavy lab schedules find it harder to maintain high GPAs — more of their grade comes from high-credit, high-difficulty courses. When planning your semester, consider the credit distribution, not just the number of classes.
Weighted vs. unweighted GPA
High schools often use a 5.0 weighted scale that adds 1.0 to AP and IB grades and 0.5 to Honors grades. This rewards students who challenge themselves with rigorous coursework. However, most colleges recalculate an unweighted GPA on the standard 4.0 scale when evaluating applications, so an unweighted 3.8 from tough courses often looks better than a 4.5 weighted from the same school. Check each college's policy before assuming the weighted GPA is what they'll see.
How your semester GPA affects your cumulative GPA
Your cumulative GPA is the running credit-weighted average of every semester. Early semesters have an outsized effect because they represent a larger fraction of your total credits. After 90 credits, even a perfect 4.0 semester in a 15-credit load can only move a 3.0 cumulative GPA to 3.09. Conversely, a poor first semester at 30 credits total can be raised significantly by strong performance in subsequent semesters. The projection feature in this calculator shows exactly how each outcome scenario affects your overall GPA.