It would be perhaps more enlightening to see the percentage of students that are in a school that offers it rather than the percentage of schools. I don't see that figure in this table, but it does show 4.7% of high school students enrolled in calculus.
That's an exaggeration. As of 2018, 65% of public schools in the US offer Calculus:
https://nces.ed.gov/programs/digest/d21/tables/dt21_225.72.a...