The study also found that 79% of HR directors are very concerned about losing their top performing staff.
The study of 200 UK HR directors says that employees are the single most important commodity for organisations, and any loss in resourcing, particularly of a valued employee, can have serious consequences on growth and profitability.
Phil Sheridan, managing director, Robert Half said: "Top performers are instrumental in helping organisations grow. However, it is all too common for companies to wait until they receive resignations in order to enhance their retention efforts, but by then it is often too late to keep those key staff.
"Losing one in every five employees can have devastating effects on company operations."
Sheridan added: "The new year has always been a popular time for employees to move jobs, largely the result of resolutions coupled with annual bonus payouts.
"However, when businesses are able to maintain continuity among their teams, they are in a better position to navigate through the uncertain economic landscape and achieve success.
"Unfortunately, it's not always possible to retain your best and brightest. However, by making sure employees are happy though regular communication, company updates and encouragement, you can ensure that your company isn't hit with that mass exodus."
