The amount of time to acquire a PhD depends on a student's performance and not the nature of the program. In fields like medicine, a two-year PhD is impossible to acquire. Although possible two-year completion times appear more often at online universities, students who pursue an online doctorate may have difficulty making this degree appear positive to prospective employers.

The Traditional PhD

Most PhD students at reputable, in-person universities do not finish their program in two years. According to the PhD Completion Project, only 4.5 percent of PhD students from all fields acquire their degree in three years, and based on completion trends the number of students who acquire their degree in less time would be even smaller. Doctoral degrees in medicine, law and business require internships and other supervised work, and these requirements preclude a completion time of two years or less.

The Online PhD

Private, online universities occasionally offer doctoral programs with a possible two-year completion time. They focus on distance coursework followed by in-person research presentations if the program is reputable. However, the employer bias against online degrees decreases their value. In studies analyzed by Norina Columbaro and Catherine Monaghan in 2009, employers widely preferred candidates with a traditional, in-person degree by a margin of 90 percent or higher in most cases.

The Accelerated-track PhD

Under certain circumstances a candidate may create an accelerated-track PhD program in the sciences or humanities, but this requires foresight and work outside the program. Greg Mankiw, a professor of economics at Harvard University, graduated with a PhD in two years by acquiring graduate credits as an undergraduate and then doing research while working as an economist. His employer during that time became his academic advisor when he returned, which also accelerated his track to the PhD.