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.
See? This is why I’m confused!
All part of being a Doctor Who fan.
For naming purposes, we really only number the ones who are the “main character”, so John Hurt and Jo Martin don’t get numbers per se, and David Tennant gets 10 and 14 because those are treated as distinct and separate characters, while 10’s “fake-out” doesn’t result in a distinct incarnation so doesn’t get numbered separately.
Basically, lots of asterisks in the numbering, but the numbers are more for fans being able to easily differentiate them in conversation than anything. They’re only rarely referred to in the show itself.