The time it takes to become a detective will vary depending on the type of detective you want to be and the agency you want to work for.
Generally, becoming a public or police detective requires first becoming a police officer. This usually requires graduating from high school and joining the academy. Earning an associate or bachelor’s degree in psychology, criminal justice, criminology, or related areas is usually preferred by most agencies, though not always a hard requirement. Police academy programs generally last six to eight months, after which officers must typically gain four or five years of experience before they can take a promotional exam to become a detective. Some police departments allow officers to substitute a college degree for a year of experience. Overall, it can take anywhere from five to eight years to be promoted from a police officer to a detective.
On the other hand, becoming a private detective usually does not have specific education requirements, but may often require previous experience in criminal justice or related areas.