|Original Incarnation||New Incarnation||Change||1||2||3||4||5||6||7||8|
|1 Hartnell||2 Troughton||Rejuvenation
|2 Troughton||3 Pertwee||Unknown||1||0||1||0||1||0||1||0|
|3 Pertwee||4 T. Baker||Regeneration||2||1||2||1||2||1||2||1|
|4 T. Baker||5 Davison||Regeneration||3||2||3||2||3||2||3||2|
|5 Davison||6 Baker||Regeneration||4||3||4||3||4||3||4||3|
|6 Baker||7 McCoy||Regeneration||5||4||5||4||5||4||5||4|
|7 McCoy||8 McGann||Regeneration||6||5||6||5||6||5||6||5|
|8 McGann||* Hurt||Regeneration||7||6||7||6||7||6||7||6|
|* Hurt||9 Eccleston||Unknown||8||7||8||7|
|9 Eccleston||10 Tennant||Regeneration||9||8||8||7||9||8||8||7|
|10 Tennant||10 Hand Tennant||Regeneration Energy||10||9||9||8|
|10 Tennant||11 Smith||Regeneration||10||9||9||8||11||10||10||9|
This is a table of possible regenerations and that 10’s non-regeneration does not count.
All Odd numbers assume that Pertwee was the first Regeneration.
All Even numbers assume that Baker was the first Regeneration.
1 and 2 assume that Hurt Eccleston was a regeneration and that 10’s non-regeneration does not count.
3 and 4 assume that Hurt Eccleston was not a regeneration and that 10’s non-regeneration does not count.
5 and 6 assume that Hurt Eccleston was a regeneration and that 10’s non-regeneration counts.
7 and 8 assume that Hurt Eccleston was not a regeneration and that 10’s non-regeneration counts.
All of these counts make the assumption that Hartnell to Throughton was not a regeneration. He uses a “rejuvenation” machine which has been said to not count as a rejuvenation. An error on my part in thinking there was a “machine”, looking further into the “rejuvenation” factor it seems it was something referenced later in the series after Hartnell became Throughton as to what happened to the Doctor. This was before the concept of regenerations became official and it might just be another term for the word in which case all counts could be increased by 1 to account for this.
Since Throughton to Pertwee is not shown specifically to regenerate, this creates a possible discrepancy in the number of regenerations based on how the writers decide to interpret it. This is why a second count exists where he’s not considered the first regeneration.
A second discrepancy is created by the change from Hurt to Eccleston since it isn’t shown on-screen and we as of yet do not know what happened to cause it, it is possible that a rejuvenation machine could have been used and Eccleston is a younger version of Hurt. Which could explain why he’s such a dark doctor in comparison to most others. This is why a count exists that both includes and excludes this as a possibility.
A third discrepancy exists surrounding the 10’s hand. 10’s regenerative process starts and he uses some energy to heal himself and then puts the rest into the hand. Since the energy was triggered it’s possible to say that was a regeneration. However since the energy didn’t completely take over and change him then the biological counter for regenerations may not have increased. So this means that it’s possible to count it either way based on how you want to interpret it.
At Smith the lowest possible number of current regenerations is 8. While the maximum number is 11. Since Moffat has commented that we’ve “missed” something I believe that perhaps the number is closer to 8 than 11.
Another factor that may drastically change the count is how the writers decide to interpret River Song saving the Doctor after she poisoned him. Assuming she only regenerated twice that would mean she had 10 regenerations left when she gave them up to save the Doctor. Making the assumption that only one life was needed to cure the poison and River couldn’t actually control how many regenerations she could give this might mean he has 9 additional regenerations left to him that was never addressed by the series as it stands.
EDIT: Based on more information I’ve gathered, the 5th Doctor stated he has regenerated 4 times previously. We’ve seen based on the 50th that the War Doctor is both regenerated into and out of. Based on this information there are only two possible number of regenerations left, 1 or 0.