In the Doctor Who universe, how many times can a time lord normally regenerate?

In the Doctor Who universe, a Time Lord normally has the ability to regenerate a total of 12 times. This limitation was established in the classic series and has been a longstanding rule within the show's mythology. Each Time Lord is granted 12 regenerations, allowing for a total of 13 incarnations. However, this rule was later addressed and altered in the modern series, granting the Doctor additional regenerations through various means, ultimately circumventing the original limitation.