I will be addressing the TV series mentions – off hand remarks that led me to my conclusion, So any book or comic or other part of the Who universe (Whoverse) does not count. I’m ignoring a reference to 507 in an episode of The Sara Jane Adventures because it was in response to “is there a limit”, and I think it was a throw away response.
Of course, The Doctor can have as many lives or regenerations as is needed for the TV show to keep going. After all that is why they were created.
As any fan knows a Time Lord (male or female descriptive) naturally has 13 “lives” they can live by regenerating when they are near death.
In the Christmas special and final episode of Peter Capaldi’s Doctor “Twice Upon a Time”, we learned that they can choose not to regenerate if they don’t want to.
In Season 7s “Let’s Kill Hitler”, we learned that a Time Lord can give some of their regenerations to another Time Lord. Or in this case “use” them to save a Time Lord from dying. It was not said that she “gave” them. I don’t believe that Dr. River Song gave him 10 regenerations, but just kept him from dying, but could not control the regeneration energy output. – Otherwise the Time Lords would not have had to give him any in “The Time of the Doctor”.
In season 7’s “The Angels Take Manhattan”, and in season 10’s “The Witch’s Familiar” we found out a Time Lord can give some of his regeneration energy to someone else to heal wounds or stave off death. It is unclear if you need to be a Time Lord or similar being, but we have never seen The Doctor do it to any of the other sick or dying he has encountered.
With all of this regeneration information in mind we don’t know how many lives were given or taken from The Doctor in these episodes.
Now to the good stuff.
- If we start with the original 13 lives of a time lord and assume he was given another 13 in the season 7 Christmas special “The Time of the Doctor” by the Time Lords that makes 26. We can assume 13 more were given because Rassilon makes a sarcastic reference to this in ‘Hell Bent’ — “How many regenerations did we give you again? I’ve got all night!” This is definitely more than one, but still unknown.
- This is the one most people have not noticed… In season 6 episode 4 “The Doctor’s Wife”, while the TARDIS is occupying a humanoid body, she says “I’ve got about 30 now!” while they were talking about old control rooms. We know the TARDIS gets a new control room when she gets a new Doctor.
So, this 30 number collaborates the 26 of a Doctor with 2 full lifespans of a Time Lord, plus or minus some regeneration energy and the ability to create a new control room just a few times for other reasons than a new Doctor regeneration.
So, The Doctor has approximately 26 lives.