While those who work in an office may work the typical 9:00 a.m. to 5:00 p.m. business hours from Monday to Friday, many Americans have jobs that run outside these hours. In fact, about 15 percent of Americans, on any day, are working the night shift, also called the third shift.

Three working shifts aren't just limited to factory jobs. Hospitals and emergency services, customer service call centers, hotels, janitorial firms, and any store that's open late at night all require people to work different shifts. While shift work can vary with each organization, the typical model for a 24-hour operation includes three shifts of eight hours each.

First Shift Hours

A company's first shift is usually the same as normal business hours, running from 9 a.m. to 5 p.m., or more commonly from 8 a.m. to 4 p.m. It's also called the day shift. If you are working the first shift, your life will generally be aligned with the lives of most of your friends and family. You'll be at home for dinner, and you'll be able to socialize at night, without the socializing interfering with your job. On the downside, you will have the same commute to work as that of most other workers, so traffic congestion means you need to spend more time on the road getting to and from work.

Second Shift Hours

The second shift follows the first shift and normally runs from 4 p.m to midnight. It's also called the afternoon shift, or the swing shift. Anyone working the second shift can often make a bit more money than those working the first shift. Companies pay a small shift premium to these workers, primarily because it's harder to find people to work these hours. Working the second shift means that you'll be going to work just before everyone else gets home and you'll get home after most people have gone to bed. Dinners and evenings with friends and family will have to wait until your days off.

Third Shift Hours

The third shift usually runs from midnight until 8 a.m. It's also called the night shift, the midnight shift, or the graveyard shift. The shift premium for the third shift is usually a bit higher than the second shift. You'll be going home when everyone else is getting ready to go to work and you'll have to sleep during the day.

Rotating Shifts and Other Shift Variations

How a company manages its shifts is usually a matter of company policy and culture. A company with fixed shifts keeps everyone on the same shift until they apply for, and are approved for, a change. Other companies use a rotating shift schedule, where you would work the first shift for two or more weeks, then the second shift for the same period of time, then the third shift and then back to the first shift again.

Night Shifts and Your Health

Working night shift hours can have adverse effects beyond interfering with your social life. In 2016, biologists at MIT found a link between working night shifts and an increased risk of cancer. This is likely due to the fact that humans have evolved to sleep during the night when it's dark, and to be up in the day, when it's light. Working the night shift turns this schedule on its head, interfering with the body's circadian rhythms.

A 2016 study by Brigham and Women’s Hospital and the Harvard Medical School found that women who work rotating night shifts for more than 10 years had a 15- to 18- percent increase in their risk of developing heart disease, compared to women who did not work these hours.