He e-mailed his counselor in early January to ask about receiving his unofficial transcript, which would show GPA and class rank. Due to Covid craziness, he was told that would not be available until much later in the month. Because he is a freshman he’s never even seen his HS GPA so far. Not wanting to hold up the application, just wanting to get it out of the way before getting too deep into spring semester, he just estimated. He figured top 10% for sure, put himself at the bottom of that 10%, then gave himself the same boost his HS would for being in honors. So, as you can see, it’s an incredibly exact science.
Seriously, don’t overthink this. USNA will not be consulting with the NSA to figure out how close your estimate was. Best of luck with your application! Hope you get good news this spring!