A weighted GPA rewards harder courses by adding quality points to them. Howard County Public School System Policy 8020 spells the mechanism out: multiply the quality points of each final grade by the credits of the course, sum the results, divide by the total credits — and grant 0.5 additional quality points per credit for honors courses and 1.0 for AP or GT courses, but only where the grade is A, B or C. That last condition matters.
A failed AP course earns its student nothing extra, which is why the two credit fields here ask only for credits passed with C or better. The boosts are fields rather than constants because districts disagree. Broward grants 1.0 for honors; AP/AICE/IB gets 2.0 only with the corresponding exam taken, otherwise 1.0, always at C or better.
If your school publishes different numbers, put them in and the arithmetic stays right. What this page does not do is work course by course. It takes the totals, so it handles any number of courses but shows no per-course breakdown and no way to strike a single class.
It also reports one number, the weighted GPA. For the unweighted figure, set both credit fields to zero: what remains is grade points over credits. A prior record and the cumulative GPA belong to the plain GPA calculator instead.