For many, four years seems about the right span of time. The decision should be driven by your happiness, the company’s prospects and your career path.
"If you are happy, staying at a company for an extended amount of time is a reasonable decision. However only in rare circumstances are an employer and an employee a good match for a really extended period of time. That being said, environment often trumps economics if you really enjoy where you work."
See on blog.wealthfront.com