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.
They call Hurt’s character “The War Doctor”, but as I recall he made the decision himself to not go by “Doctor” because of what he knew he had to do, so it’s almost like he abdicated the title.
The metacrisis doctor was a kind of botched regeneration, which ended up half human (presumably on his mother’s side), and thus doesn’t count either.
Tennant’s doctor in these three episodes is seen as a distinctly different doctor than 10, just “with the same face”, so he counts as 14
We still don’t know whether this bi-generation thing is stable at all. Maybe we won’t see David Tennant as often as we think we will.
Jenny’s case is unusual, as she was a clone of the Doctor, who the Doctor treated as his daughter. And you know the inside joke, that the actress who played Jenny (Georgia Moffett) was the real-life daughter of the actor who played the 5th Doctor. And the further meta-joke, which is that David Tennant eventually married the actress who played his clone/daughter.
I’ve seen Alabama family trees more straightforward than this, but I suppose that’s just what happens with long-term, transdimensional, transuniversal time and space travel.