What Is a PhD?

A Doctor of Philosophy, often known as a PhD, is a terminal degree—or the highest possible academic degree you can earn in a subject. While PhD programs (or doctorate programs) are often structured to take between four and five years, some graduate students may take longer as they balance the responsibilities of coursework, original research, and other degree requirements with raising families or working full time. 

With a PhD, you may find opportunities to work as a university professor, a researcher in a commercial or government laboratory, a consultant, or a subject matter expert (SME). If you have the intellectual curiosity and dedication, earning a PhD can be a rewarding experience. In this article, we’ll go over what it takes to earn a PhD, the requirements to apply for a PhD program, and other factors worth considering.

Learn more: What Does ‘PhD’ Stand For?

PhD: Key facts

Generally, students begin their PhD after earning a bachelor’s degree and a master’s degree. However, some doctoral programs may offer you the chance to earn your master’s while pursuing your PhD, so that may not be an admissions requirement.  

What can you get a PhD in?

It’s possible to earn your PhD in a number of academic disciplines, including the natural sciences, humanities, arts, and social sciences. The 2021 Survey of Earned Doctorates, from the National Center for Science and Engineering Statistics, offers a numerical breakdown of actual degrees earned in broad academic fields [1]:

• Engineering: 10,240

• Biological and biomedical sciences: 8,149

• Social sciences: 4,878

• Physical sciences: 4,693

• Psychology: 3,797

• Computer and information sciences: 2,361

• Health sciences: 2,331

• Mathematics and statistics: 2,012

• Agricultural sciences and natural resources: 1,334

• Geosciences, atmospheric sciences, and ocean sciences: 1,064

• Education: 4,252

• Humanities and arts: 4,137

• Business: 1,392

• Other fields: 1,610

Depending on the university you attend, you may find that the broad academic fields above break down into more specific disciplines. For example, within a physical science department, you might get a PhD in physics or chemistry. Within an engineering department, you might get a PhD in electrical or mechanical engineering. Philosophy, theology, history, or English might fall within a humanities department, while economics or social work could fall within a social sciences department. Marketing could be a specific PhD major within a business department.

In terms of your PhD coursework and research, you will likely be expected to concentrate in some area of your larger subject. For example, PhDs in biology may focus on biochemistry or biostatistics, whereas a PhD in English may concentrate on twentieth-century American literature. 

Requirements to get a PhD

PhD programs typically require at least two years of advanced coursework, as well as comprehensive exams, and the successful completion of a dissertation. Let’s break that down on a year-by-year basis: 

• Years 1 and 2: Take classes to develop advanced knowledge in your subject area. 

• Year 3: Study for and successfully pass your comprehensive exams. 

• Years 4 and 5: Research, write, and defend your dissertation. 

Once you have successfully passed your comprehensive exams, you’re typically considered “All But Dissertation” or ABD, which signals that you’ve finished everything in your doctoral program except your dissertation. 

Research supervisor 

PhD students often choose a faculty member who specializes in their area of interest to serve as the research supervisor. It can help to identify professors or programs that will support your research endeavors before applying, so you can establish a relationship with your potential research advisor early. 

PhD costs 

The average cost of a PhD program in the US is $106,860, though that figure can differ based on the type of institution you attend and what you study [2].

Reasons to get a PhD

Earning your PhD can be an immensely rewarding experience, but the degree can be a big commitment, requiring significant time, money, and work. 

Here are some more reasons you may want to pursue a PhD:

• Become a subject matter expert in a particular field.

• Conduct the research you are passionate about.

• Develop transferable skills that can help in your professional life. 

• Make a difference in the world with new research.

• Make connections with scholars in your academic community.

• Open up career avenues in academic and research work.

Completing a PhD can reveal to employers that you possess a wide range of competencies that are valued in both academic and non-academic settings. 

PhD salaries

PhD holders earn a median weekly income of $1,909 compared to master’s degree holders, who earn a median weekly income of $1,574, according to the US Bureau of Labor Statistics (BLS) [3]. They may also experience lower percentages of unemployment. The unemployment rate for PhD graduates is 1.5 percent compared to master’s degree holders at 2.6 percent [3].

Requirements to apply to a PhD program

PhD programs expect you to meet several requirements before enrolling. Here are some examples of common requirements:

• Have an undergraduate degree, usually with at least a 3.0 overall GPA.

• Have a master's degree, though some programs may not require it.

• Take the Graduate Record Examination (GRE) and achieve a minimum score.

• Submit a sample of your academic writing.

• Submit your CV.

• Provide letters of recommendation, which should ideally come from academic faculty members who can speak to your research or intellectual abilities.

Requirements differ by program and school, so take time to become familiar with the entry requirements of universities where you’re interested in applying. Admissions staff or departmental staff should be able to give you specific information about their admissions requirements.

If a program is interested in you, based on your application, you may have to complete an interview. The university representatives that interview you will look at your motivation, how prepared you are, and how suitable you are for acceptance into the doctoral degree program.

PhD vs. other terminal degrees

Terminal degrees are the highest degree available in a field of study. While the PhD is the highest academic degree you can earn in a field of study, a Juris Doctor (JD) is the highest degree you can earn in law, and a professional degree, such as a Doctor of Medicine (MD) or a Doctor of Veterinary Medicine (DVM), is the highest degree you can earn in these medical professions. 

Learn more: What is a Terminal Degree and Do You Need One?  

Professional doctorates are a different category of doctorate degree. They are usually intended for professionals already working in a field who want to pursue advanced training in their area. The main difference between a professional doctorate and an academic doctorate has to do with subject matter and research. While PhDs are interested in conducting new research, professional degree students take existing models and knowledge and apply them to solve problems. Professional doctorates are also designed to prepare learners for careers in a certain industry rather than academia.  

Examples of professional doctorates include:

• DBA (Doctor of Business Administration)

• DNP (Doctor of Nursing Practice)

• EdD (Doctor of Education)

• DPH (Doctor of Public Health)

Is someone with a PhD a doctor?

You can use the salutation "Dr" to address people who hold doctorates, including PhDs and other professional degrees. The word "doctor" comes from the Latin word for "teacher," and PhDs are often professors at universities. While it has become more common to refer to medical doctors as “Dr,” some professors use the honorific when addressing students and in professional settings.

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