There is only one GPA formula, and every calculator on this site is a different surface on the same idea: a credit-weighted average of grade points. The formula matters because the intuition is wrong. Most students assume a GPA is the average of their letter grades. It isn't. It's the average of the grade points those letters map to, and the average is weighted by the number of credits each course was worth, so a 4-credit B+ moves your GPA about four times as much as a 1-credit A. Everything else in the GPA landscape — weighted versus unweighted, semester versus cumulative, plus-minus versus whole-letter grading — is a variation in the inputs, not the formula. This page walks through the math once, points at the calculators that run each variation, and flags the places where school-specific policies make the inputs differ from the national defaults. The goal is that by the end, you can reproduce your transcript's GPA on the back of an envelope and spot a calculator's wrong answer when you see one.
The formula, in one line
GPA equals the sum of (grade point × credit hours) divided by the sum of credit hours. That's the whole thing. The numerator is often called quality points on transcripts, and summing it is the only step that actually requires any care — every letter needs its matching grade point, and every course needs the right credit-hour value.
If a semester had an A in a 4-credit course, a B+ in a 4-credit course, an A− in a 3-credit course, a B in a 4-credit course, and an A in a 1-credit PE elective, the quality points are 16.0, 13.2, 11.1, 12.0, and 4.0, summing to 56.3. The credit hours sum to 16. The GPA is 56.3 divided by 16, which is 3.52. The hardest part of the arithmetic is remembering that the PE course gets weighted just like the others — a 1-credit A contributes exactly 1 credit's worth of A to the average, not the whole-letter weight your eyes want to give it.
The 4.0 scale and its variants
The standard US undergraduate scale maps A to 4.0, B to 3.0, C to 2.0, D to 1.0, and F to 0.0. Most schools extend this with plus and minus grades: A− is 3.7, B+ is 3.3, B− is 2.7, C+ is 2.3, and so on in 0.3 increments. A few schools cap A+ at 4.3 to leave headroom above an A, but this breaks the 4.0 ceiling and is uncommon on official transcripts.
High schools commonly add Honors bonuses of +0.5 and AP or IB bonuses of +1.0 on top of the base grade point, so an A in AP Chemistry becomes 5.0 on a weighted transcript and stays 4.0 on an unweighted one. Some districts use a 100-point scale instead, mapping 93–100 to A, 90–92 to A−, and so on; the grade-point conversion is the same, just applied after the cutoffs. When in doubt, the grading scale is usually printed on the back of the transcript — and if two transcripts look inconsistent, checking which scale each school uses is almost always the right first step.
Weighted vs unweighted
Weighted GPA rewards course rigour; unweighted GPA reports performance on a common scale. Both numbers are defensible, and admissions offices routinely compute both. The weighted GPA is what appears on most high school transcripts by default because it reflects the difficulty of the courses taken, but it's the unweighted number that lets an admissions office compare applicants from different schools with different weighting policies.
The University of California's a–g recalculation caps honors semesters at eight, drops non-academic electives, and computes a UC-only GPA that sits between weighted and unweighted. The Common App's school report asks for weighted and unweighted separately when the school provides both. A student comparing their own number to a published middle-50% admitted range needs to know which one the school published. Running both numbers through the weighted and unweighted GPA calculators on this site takes about two minutes and eliminates a lot of the confusion that otherwise creeps into the college search.
Cumulative vs semester
Semester GPA is the single-term calculation; cumulative GPA combines every term you've completed into one running average. The tricky part about cumulative is that you can't average GPAs without knowing the credit counts behind them. Fall was 3.8 and spring was 3.4 doesn't mean the year was 3.6 — it means you need fall's credits and spring's credits, and the combination has to be credit-weighted.
If fall was 18 credits and spring was 12, the year GPA is (3.8 × 18 + 3.4 × 12) divided by 30, which works out to 3.64. The cumulative GPA calculator asks for both the prior GPA and the prior credit count because the number alone can't carry forward correctly. This is the single most common arithmetic mistake on grade math; dozens of emails to this site over the years have come from readers who got the wrong answer exactly this way.
How admissions offices actually read it
A GPA in isolation is almost never the decision. Selective admissions read GPA in context: against the school's distribution of GPAs (is this near the top of the class?), against the rigour of courses taken (did the student take AP Chemistry or regular Chemistry?), and against the trajectory (improving or declining over four years). A 3.9 with four APs is often read more favourably than a 4.0 with no APs. This is why the weighted number exists and why the unweighted number exists — they answer different questions.
The published middle-50% GPA at a selective school is a useful calibration but not a predictor: plenty of applicants below that range are admitted every year, and plenty inside it are rejected. The acceptance-probability calculator on this site gives a numerical baseline based on how an applicant's GPA and test scores compare to the school's published middle-50% ranges, but it is explicitly a baseline, not a forecast — the parts of the application that matter most to admissions (essays, recommendations, extracurricular depth) aren't things arithmetic can capture.
Common errors and how to spot them
The five errors that show up most often in GPA math: averaging GPAs without credit weights, treating a 1-credit A as a full A in a large course, forgetting that A− is 3.7 rather than 3.67, applying weighted bonuses on an unweighted scale (producing a number above 4.0 on what's supposed to be the 4.0 scale), and counting pass-fail courses in the GPA denominator when most schools exclude them.
The way to check any suspicious GPA is to do it by hand: list every course, convert each letter to a grade point, multiply by credits, sum, divide. The calculator on this site and the one on your student portal should agree to within rounding. If they don't, the difference almost always traces to one of those five errors. Email the registrar's office (not your teacher) if a transcript number still looks wrong after the hand calculation agrees with the calculator — the registrar is the authoritative source and usually responds within a few business days with either a corrected transcript or an explanation of which rule applied.
The calculators that run each version
If you want to run your numbers through the arithmetic rather than the napkin, the GPA calculators on this site cover every common version: weighted and unweighted for any single term, semester GPA for this term in isolation, cumulative GPA for combining terms, an honors GPA threshold calculator, a grade-needed-to-pass calculator for when you want to know what a final has to deliver, a class-rank percentile calculator for converting rank into the percentile that admissions offices actually read, and a pass-fail impact calculator for deciding whether to take a course P/F. Each calculator prints the formula it used and a worked example of the arithmetic, so you can always verify.
Closing
GPA math is simple once the formula is visible. The calculators handle the arithmetic, the explanatory prose under each one spells out the variations, and the blog posts walk through the three or four places where the formula produces answers that feel wrong until you see why. If anything on any of these pages disagrees with your registrar's number, write to us and we'll look at it.