If you follow the current timeline, it should go-
Hurt->Eccleston->Tennant->Tennant->Smith->Capaldi->Whitaker->Tennant->Tennant/Gatwa
Hurt was the real 9th doctor, but we call Eccleston the 9th doctor. And (if I get this all right) Tennant regenerated as himself twice, so he should be the 11th, 12th, 15th and Doctor 16 and a half. But people call him the 10th doctor. And Jodie Whitaker should have been the 14th Doctor, but people call her the 13th Doctor. And then Tennant came back and then there was the bigeneration of him and Gatwa.
And just to add to it all, there’s also a female clone of Tennant out there somewhere.
Is anyone else as confused as I am?
EDIT: Oh god, I just realized it gets even more confusing because now there’s all the Doctors before Hartnell.
Hartnell will always be the First Doctor, no matter who that character was before that. So we can call Jo Martin the Zeroth Doctor, as some have, and number the rest negatively if we ever learn about them, or we can just refer to them by a descriptor, like the Fugitive Doctor.
It’s also unclear now when exactly the character first took the name “Doctor”, but what is more clear is that the numbering is a convention for the viewers, not really for the characters themselves.