* Field of study: Some fields, like humanities, often take longer than others, like some STEM fields.
* Program requirements: Universities and programs have different requirements for coursework, research, and dissertation length.
* Individual student's progress: How quickly someone conducts research, writes, and defends their dissertation significantly impacts their timeline.
* Funding and other commitments: Students with teaching or research assistantships might have a slightly slower pace than those solely focused on their research.
While some students might finish in 4-5 years, it's not uncommon for a full-time PhD to take 6-8 years, or even longer. Thinking of it as a 5-7 year commitment is a reasonable expectation. Anything shorter is a bonus, and anything longer shouldn't necessarily be considered unusual.