It Depends on the Scale
The highest possible GPA depends on the scale that you are using. The commonly used 0-4 scale (also known as an unweighted scale) caps the highest score at 4.0, but weighted scales like the 0-4.5 or 0-5 scale make higher GPAs possible.
Typically, high schools that use weighted GPAs opt for the 0-5 scale that makes 5.0 the highest possible grade. A GPA higher than 5.0 is rare, but school point systems are occasionally structured so that students taking advanced classes can rack up bonus points. One student even managed to land a stunning 10.03 GPA by taking 17 advanced classes at a school that awarded bonus points.
If the different GPA scales seem a little confusing, check out our guide on how to calculate GPA for a straightforward explanation of weighted and unweighted GPAs.