The regulation length of an NHL overtime period in the regular season is 5 minutes.
If the score is tied after three 20-minute regulation periods, the teams play a sudden-death overtime. The first team to score wins immediately. Modern regular-season overtime uses three skaters and a goaltender per side, creating more open ice and scoring chances than regulation play.
The NHL brought back regular-season sudden-death overtime for the 1983–84 season. The league later changed the format from four-on-four to three-on-three beginning in 2015–16. If neither team scores during the five-minute period, the game proceeds to a shootout, unlike a playoff game, where overtime periods continue until someone scores.
A common mix-up is confusing regular-season overtime with playoff overtime. NHL playoff overtime periods are 20 minutes long and played five-on-five, while regular-season overtime lasts only five minutes and can end in a shootout.