How a GPA is actually worked out
A GPA is a credit-weighted average, not a plain average of your letter grades. Each grade converts to grade points, those points are multiplied by the credits the course carries, and the total is divided by the credits you attempted.
The multiplication by credits is the step most people skip, and it is the one that changes the answer. A B in a four-credit lab course drags far harder than an A in a one-credit seminar lifts.
A worked example
| Course | Grade | Points | Credits | Quality points |
|---|---|---|---|---|
| Chemistry | A− | 3.7 | 4 | 14.8 |
| Calculus | B+ | 3.3 | 4 | 13.2 |
| English | A | 4.0 | 3 | 12.0 |
| Seminar | B | 3.0 | 1 | 3.0 |
| Total | 12 | 43.0 |
43.0 quality points over 12 credits gives a GPA of 3.58. Notice that a straight average of the four grade points would have given 3.50 — the credits are doing real work.
Unweighted versus weighted
An unweighted GPA caps every course at 4.0, so an A in gym is worth exactly what an A in AP Physics is worth. A weighted GPA adds a bonus for harder courses, most commonly +0.5 for Honors and +1.0 for AP, IB or dual enrolment, which is how students end up reporting a 4.3 or a 4.7.
There is no national standard for weighting. Some districts weight only AP, some cap the bonus, some use a 5.0 scale throughout. This is why selective colleges almost always strip your weighting out and recalculate on their own scale using core academic courses only.
What usually does not count
- Pass/fail courses earn credit but carry no grade points, so they are left out of the average entirely.
- Withdrawals normally show as W and are excluded, though a late withdrawal can post as WF and count as an F.
- Transfer credits often bring the credit across but not the grade, so they change your credit total without moving your GPA.
- Incompletes sit outside the calculation until the grade is finalised.
Why your GPA gets harder to move over time
Cumulative GPA is the same formula applied to every credit you have ever taken. A student with 15 credits at 3.0 who then earns a perfect 4.0 term of 15 credits lands at 3.50. The same perfect term after 90 credits at 3.0 only reaches 3.14. Early terms are cheap to fix and late terms are expensive, which is the single most useful thing to know about GPA management.
If you are converting a percentage score into a letter first, the grade calculator will handle the weighting of assignments and tell you what you need on a final.