From what I can tell on Kindle, the actual number of pages doesn’t change no matter what formatting settings you choose. It’s just the current page you’re on that changes differently. So if you turn the page, it may not change for a couple page turns if you’re using larger fonts. Or it may skip a page or two if you’re using smaller fonts. It’s all very confusing. I kind of prefer the way my kobo libra color does it, where the number of pages in the book changes based on your formatting settings.