Most students can recite their current GPA to two decimal places — and have no idea where the number actually comes from. The confusion is understandable, because GPA is not a simple average of your percentages. It is a weighted average built on three steps: convert each letter grade to a number (usually A = 4.0, B = 3.0, C = 2.0, and so on), multiply that number by the course's credit hours, add those products together, then divide by the total credit hours attempted. A four-credit class literally counts twice as much toward your GPA as a two-credit class — which is why a single bad grade in a heavy lab course can drag down an otherwise strong semester.
Percentages add another wrinkle. Some professors convert raw scores to letter grades on a curve, others use fixed cutoffs (90 = A−, 80 = B−, and so on), and a few mix in plus/minus modifiers that map to fractional GPA points (A− = 3.7, B+ = 3.3). The same 87% can be a B+ in one class and a B in another, which is why two students with identical percentage averages can have meaningfully different GPAs. Knowing your school's exact scale — usually published in the registrar's handbook — is the first step to predicting how a future grade will move your number.
The fastest way to internalize this is to plug your own grades into a calculator that does the credit-hour weighting for you. Our free Homework Calculator handles percentages, class averages, and GPA in one place — enter your courses and credit hours, and it shows you exactly how each grade contributes.
And if you want to set a target GPA for the semester and back-solve what grades you need to hit it, the Student Reset Planner includes a goal-setting worksheet that pairs GPA targets with a weekly study plan so the math actually turns into action.