Which grading convention runs behind each calculator, why it is a convention rather than a national rule, and what happens when one turns out to be wrong for your school.
There is no single, federally mandated GPA scale in the United States. Every school and district sets its own grading policy, and this site has to be honest about that instead of presenting one table as if it were law. This page lists exactly which convention each calculator uses, where that convention comes from, and how often it gets rechecked.
The GPA calculator, semester GPA calculator, cumulative GPA calculator, college GPA calculator and high school GPA calculator all default to the 0-to-4.0 grade-point scale used by most American high schools and colleges: A = 4.0, B = 3.0, C = 2.0, D = 1.0, F = 0.0, with plus and minus grades filling the gaps in between (A- = 3.7, B+ = 3.3, and so on). That scale is a long-standing convention, not a standard set by a federal agency, which is why some schools score an A+ as 4.3, some drop plus and minus grades entirely, and a handful still report on a straight 100-point scale. The math itself, multiplying each grade's point value by the course's credit hours to get quality points, then dividing total quality points by total credit hours, is arithmetic, not convention, and does not vary by school.
The weighted GPA calculator defaults to adding 0.5 grade points for an honors course and 1.0 for an AP or IB course, which is the bonus scale used by a large share of U.S. high schools. It is not set by the College Board, the organization that administers AP exams and course curricula; the exam scoring and the in-school weighting bonus are two separate things, and individual districts decide how much extra weight, if any, an AP or IB grade gets in the school's own GPA calculation. Some schools use a flat 1.0 bonus for both honors and AP, some use no weighting at all, and some cap weighted GPA at 5.0 rather than letting it run higher. The calculator's default is a starting point for estimating your own number, not a claim about what your specific school does.
The grade calculator and final grade calculator solve a weighted-average equation, current grade times its share of the total plus the final's score times its share equals the target grade, and rearrange it to isolate the unknown. There is no outside convention to cite here: it is the same algebra a student could do by hand from a syllabus that states how much the final is worth. The one judgment call the calculator makes is flagging when the score needed exceeds 100 percent, since that means the stated target is not mathematically reachable from the final alone, not a bug in the tool.
The fraction calculator and algebra calculator apply standard arithmetic and algebraic rules: common denominators for fraction addition and subtraction, the quadratic formula for quadratic equations, direct substitution for linear ones. These are not conventions that vary by school; they are the same rules taught in any U.S. math curriculum, and the discriminant reported alongside a quadratic result (positive, zero, or negative) follows directly from the formula rather than a judgment call on our part.
The test score calculator converts a raw questions-correct count into a percentage, then maps that percentage to a letter grade using the same 90/80/70/60 cutoffs used on the GPA scale page. Those cutoffs are widespread but not universal: some schools use a 93 percent cutoff for an A rather than 90, and some grade on a curve that moves the cutoffs entirely. Treat the letter the calculator returns as an estimate against a common default, not your actual recorded grade.
The IQ percentile calculator converts a score you already have into a percentile using the normal distribution, the same statistical model modern IQ tests like the Wechsler scales are built on, with a mean of 100 and a standard deviation of 15. That mean-and-spread convention is set by the test publishers who standardize their instruments against a reference population; this calculator does not administer a test or diagnose anything, it only re-expresses a number you already have in percentile terms.
A calculator here can only apply the convention you select to the numbers you enter. It cannot know whether your school gives an A+ a 4.0 or a 4.3, whether your district weights an AP class by 0.5 or 1.0, or whether your registrar rounds a 92.5 up or down. Every result is a planning estimate built on a stated default, and every page on this site says so before it says anything else. The GPA scale page exists specifically to help you check your own school's policy against the common default.
The scales and formulas above are stable conventions, not figures that move with a market or a legislative session, so there is no fixed annual update cycle the way there might be for a tax bracket. We recheck each calculator's stated convention against its own description on this page whenever a guide is rewritten or a reader flags a mismatch, and the "last updated" line on the GPA scale page reflects the most recent pass.
If a calculator's arithmetic does not match what you get running the same numbers by hand, that is a bug, not a difference of opinion, and we want to hear about it through the contact form. Genuine calculation errors get fixed and the change is dated. A report that your school's grading policy differs from the site's default is not an error on our part, since the default is explicitly a common convention, but it is exactly the kind of detail we use to sharpen the wording on the page in question.
This site carries display ads through Google AdSense and a small number of affiliate links, Amazon Associates among them. That revenue has no bearing on which grading convention a calculator defaults to or what number it returns; changing a formula to make a result look more flattering would undercut the one thing this site has to offer, which is that the arithmetic is correct.
Want to know who is actually writing and checking this material? The authors page covers who is behind GPACalcTools and what gets verified before anything publishes.