The Ph.D. will require two or more years beyond that. Graduate students often receive free or reduced tuition plus a cash stipend for serving as teaching assistants in undergraduate laboratories. Exceptional students may be able to get fellowships which do not require teaching. Admission to a graduate program is not guaranteed. It depends on appropriate undergraduate preparation and performance.
Some graduate programs are much more selective than others.
Likewise, a person may be accepted as a master's candidate but not as a doctoral candidate. Many new careers combine interests, expertise and preparation in two areas. Forensic science - DNA fingerprinting in criminal cases. Science policy - an interest in the politics of health care and research. Biostatistics - statistical analysis of mortality rates, clinical data and progression of epidemics.