As an employee benefit, some employers offer a guarantee that employees may work on their personal projects during some part (usually a percentage) of their time at work. Side project time is limited by two stipulations: what the employee works on is the intellectual property of their employer, and if requested, an explanation must be given as to how the project benefits the company in some way, even tangentially.

Google is credited for popularizing the practice that 20 percent of an employee's time may be used for side projects. At Google, this led to the development of products such as AdSense. While Gmail is frequently described as a 20% project, its creator Paul Buchheit states that it was never one. Though the program's continuity has been questioned, Google stated in 2020 that it remained an active program.

Other major companies that have at one time or another offered some or all of their employees the benefit include the BBC (10 percent of employee time), Apple (a few contiguous weeks yearly), and Atlassian (20 percent of employee time). Some companies, such as LinkedIn, have experimented with more restrictive versions in which employees must first pitch their projects to receive approval to work on them during company time.

Side project time has been criticized by some academics, such as Queens College sociology professor Abraham Walker, as "exploitative" because of how it grants employers the intellectual property rights over the personal business ideas of their employees that the employer would never have requested to be worked on otherwise.

The 15% project was an initiative established by 3M. At the time of this program's implementation, the United States' workforce was composed of highly inflexible employment opportunities in rigid business structures. WWII created an existential threat to 3M as natural rubber was needed for the war effort and scientists at 3M were given the freedom to work on a synthetic rubber. As WWII ended, 3M developed an ethos, "Innovate or die," that inspired the launch of this program. This original project had some successful outcomes; for example, during this side project time, Arthur Fry invented the Post-It Note.

In 2004, the founders of Google encouraged the system. Within Google, this initiative became known as the "20% Project." Employees were encouraged to spend up to 20 percent of their paid work time pursuing personal projects. The objective of the program was to inspire innovation in participating employees and ultimately increase company potential. Google's 20% Project was influenced by 3M's program. At Google AdSense arose out of side projects. While Gmail is frequently described as a 20% project, its creator Paul Buchheit states that it was never one.

As recognition of the benefits of retaining such a scheme grew, schools have replicated this system for their students in the classroom environment. The production of such creatively stimulated, ungraded work allows for students to experiment with ideas without fear of assessment and may increase their involvement in their general studies. Around 2013, some Google employees stated that the company had discontinued 20 percent time entirely or had it reworked from its original concept. However, the company stated in 2020 that 20 percent time still exists.

The 20% Project is responsible for the development of many Google services. Founders Sergey Brin and Larry Page advised that workers "spend 20% of their time working on what they think will most benefit Google". Susan Wojcicki utilised her time to create their product AdSense. Finally, developer Krishna Bharat created Google News as an individual pursuit and hobby.^{[citation needed]}