An increasing number of employers are expecting at least three weeks notice in order to give a good reference for a former employee. This is relevant in a culture where backdoor references are prominent in the hiring process.
Likewise, an increasing number of employers prefer to hire candidates that give three or more weeks notice to a former employer.
Two factors driving the change are (a) it is another way in which a candidate can distinguish himself from other candidates, and (b) additional time is necessary to transition responsibilities due to lean staffing conditions.
Generally, we recommend giving three to six weeks notice. More time, such as six weeks, should be given when leaving a leadership role or a position with complex responsibilities or in a complex field.
