Convert your grades into a numeric scale, according to the guidelines at your school. In most schools, "A" counts as 4.0, "B" counts as 3.0, "C" counts as 2.0, "D" counts as 1.0 and "F" counts as 0.0. Some schools also give adjustments based on "+" or "-" grades, such as "A+" being 4.3 or "A-" being 3.7. Some high schools may also offer a 5.0 count for college-level classes in which you get an "A." You will have to refer to your school's guidelines for the specific scale.
Multiply your scaled grade by the number of credits you receive for the class. This gives you the number of "quality points" for that class. For example, if you received an "A" for a 3-credit class, you would multiply 4.0 times 3 to calculate 12.0 quality points.
Repeat this process for all the classes you have completed.
If you only have the GPA and credit hours for a previous semester, multiply the GPA by the total semester hours to calculate the quality points for the entire semester. Use this figure in place of quality points for each individual class of that semester. Adding this total amount or each individual amount has the same effect.
Total all the quality points and credits for the classes you have completed. This will give you the cumulative quality points and cumulative credits thus far.
Divide the cumulative quality points by the cumulative credits to calculate cumulative GPA. For example, if you calculated 346 cumulative quality points and had 99 cumulative credits, your cumulative GPA would be 3.495.