In 2016, Americans forfeited 206 million vacation days. That means that workers lost $66.4 billion worth of benefits and, according to a new study from Project: Time Off, they are likely missing out on much more, too.

Americans used to understand the importance of getting away from the office. From 1976 to 2000, the average working American took off more than 20 days a year. Starting in 2000, workers started taking fewer and fewer days off and by 2015, they only took 16 days off a year.