A growing number of smaller companies are adopting a four-day workweek. Now the results of a recent trial at Microsoft (MSFT) suggest it could work even for the biggest businesses.

The company introduced a program this summer in Japan called the "Work Life Choice Challenge," which shut down its offices every Friday in August and gave all employees an extra day off each week.

The results were promising: While the amount of time spent at work was cut dramatically, productivity — measured by sales per employee — went up by almost 40% compared to the same period the previous year, the company said in a statement last week.