The NHL has changed its playoff format numerous times over the years. What follows is a history of the various playoff formats:
1917-18 - The regular-season was split into two halves. The winners of both halves faced each other in a two-game, total-goals series for the NHL championship and the right to meet the Pacific Coast Hockey Association champion in the best-of-five Stanley Cup Finals.
1918-19 - Same as 1917-18, except that the NHL Finals were extended to a best-of-seven series.
1919-20 - Same as 1917-1918, except that Ottawa won both halves of the split regular-season schedule to earn an automatic berth into the best-of-five Stanley Cup Finals against the PCHA champions.
1921-22 - The top two teams at the conclusion of the regular-season faced each other in a two-game, total-goals series for the NHL championship. The NHL champion then moved on to play the winner of the PCHA-Western Canada Hockey League playoff series in the best-of-five Stanley Cup Finals.
1922-23 - The top two teams at the conclusion of the regular-season faced each other in a two-game, total-goals series for the NHL championship. The NHL champion then moved on to play the PCHA champion in the best-of-three Stanley Cup Semifinals, and the winner of the Semifinals played the WCHL champion, which had been given a bye, in the best-of-three Stanley Cup Finals.
1923-24 - The top two teams at the conclusion of the regular-season faced each other in a two-game, total-goals series for the NHL championship. The NHL champion then moved on to play the loser of the PCHA-WCHL playoff (the winner of the PCHA-WCHL playoff earned a bye into the Stanley Cup Finals) in the best-of-three Stanley Cup Semifinals. The winner of this series met the PCHA-WCHL playoff winner in the best-of-three Stanley Cup Finals.
1924-25 - The first place team (Hamilton) at the conclusion of the regular-season was scheduled to play the winner of a two-game, total goals series between the second (Toronto) and third (Montreal) place clubs. However, Hamilton refused to abide by this new format, demanding greater compensation than offered by the League. Thus, Toronto and Montreal played their two-game, total-goals series, and the winner (Montreal) earned the NHL title and then played the WCHL champion (Victoria) in the best-of-five Stanley Cup Finals.
1925-26 - The format which was intended for 1924-25 went into effect. The winner of the two-game, total-goals series between the second and third place teams squared off against the first place team in the two-game, total-goals NHL championship series. The NHL champion then moved on to play the Western Hockey League champion in the best-of-five Stanley Cup Finals.
After the 1925-26 season, the NHL was the only major professional hockey league still in existence and consequently took over sole control of the Stanley Cup competition.
1926-27 - The 10-team league was divided into two divisions -- Canadian and American -- of five teams apiece. In each division, the winner of the two-game, total-goals series between the second and third place teams faced the first place team in a two-game, total-goals series for the division title. The two division title winners then met in the best-of-five Stanley Cup Finals.
1928-29 - Both first place teams in the two divisions played each other in a best-of-five series. Both second place teams in the two divisions played each other in a two-game, total-goals series as did the two third place teams. The winners of these latter two series then played each other in a best-of-three series for the right to meet the winner of the series between the two first place clubs. This Stanley Cup Final was a best-of-three.
1931-32 - Same as 1928-29, except that Series D was changed to a two-game, total-goals format and Series E was changed to best of five.
1936-37 - Same as 1931-32, except that Series B, C, and D were each best-of-three.
1938-39 - With the NHL reduced to seven teams, the two-division system was replaced by one seven-team league. Based on final regular-season standings, the following playoff format was adopted:
1942-43 - With the NHL reduced to six teams (the "original six"), only the top four finishers qualified for playoff action. The best-of-seven Semifinals pitted Team #1 vs Team #3 and Team #2 vs Team #4. The winners of each Semifinal series met in the best-of-seven Stanley Cup Finals.
1967-68 - When it doubled in size from 6 to 12 teams, the NHL once again was divided into two divisions -- East and West -- of six teams apiece. The top four clubs in each division qualified for the playoffs (all series were best-of-seven):
1970-71 - Same as 1967-68 except that Series E matched the winners of Series A and D, and Series F matched the winners of Series B and C.
1971-72 - Same as 1970-71, except that Series A and C matched Team #1 vs Team #4, and Series B and D matched Team #2 vs Team #3.
1974-75 - With the League now expanded to 18 teams in four divisions, a completely new playoff format was introduced. First, the #2 and #3 teams in each of the four divisions were pooled together in the Preliminary round. These eight (#2 and #3) clubs were ranked #1 to #8 based on regular-season record:
The winners of this Preliminary round then pooled together with the four division winners, which had received byes into this Quarterfinal round. These eight teams were again ranked #1 to #8 based on regular-season record:
The four Quarterfinals winners, which moved on to the Semifinals, were then ranked #1 to #4 based on regular season record:
1977-78 - Same as 1974-75, except that the Preliminary round consisted of the #2 teams in the four divisions and the next four teams based on regular-season record (not their standings within their divisions).
1979-80 - With the addition of four WHA franchises, the League expanded its playoff structure to include 16 of its 21 teams. The four first place teams in the four divisions automatically earned playoff berths. Among the 17 other clubs, the top 12, according to regular-season record, also earned berths. All 16 teams were then pooled together and ranked #1 to #16 based on regular-season record:
The eight Preliminary round winners, ranked #1 to #8 based on regular-season record, moved on to the Quarterfinals:
The eight Quarterfinals winners, ranked #1 to #4 based on regular-season record, moved on to the semifinals:
1981-82 - The first four teams in each division earned playoff berths. In each division, the first-place team opposed the fourth-place team and the second-place team opposed the third-place team in a best-of-five Division Semifinal (DSF) series. In each division, the two winners of the DSF met in a best-of-seven Division Final (DF) series. The two winners in each conference met in a best-of-seven Conference Final (CF) series. In the Prince of Wales Conference, the Adams Division winner opposed the Patrick Division winner; in the Clarence Campbell Conference, the Smythe Division winner opposed the Norris Division winner. The two CF winners met in a best-of-seven Stanley Cup Final (F) series.
1986-87 - Division Semifinal series changed from best-of-five to best-of-seven.
1993-94 - The NHL's playoff draw was conference-based rather than division-based. At the conclusion of the regular season, the top eight teams in each of the Eastern and Western Conferences qualified for the playoffs. The teams that finish in first place in each of the League's divisions were seeded first and second in each conference's playoff draw and were assured of home ice advantage in the first two playoff rounds.
The remaining teams were seeded based on their regular-season point totals. In each conference, the team seeded #1 played #8; #2 vs. #7; #3 vs. #6; and #4 vs. #5. All series were best-of-seven with home ice rotating on a 2-2-1-1-1 basis, with the exception of matchups between Central and Pacific Division teams. These matchups were played on a 2-3-2 basis to reduce travel. In a 2-3-2 series, the team with the most points could choose to start the series at home or on the road. The Eastern Conference champion faced the Western Conference champion in the Cup Final.
1994-95 - Same as 1993-94, except that in first, second or third-round playoff series involving Central and Pacific Division teams, the team with the better record had the choice of using either a 2-3-2 or a 2-2-1-1-1 format. When a 2-3-2 format was selected, the higher-ranked team also had the choice of playing games 1, 2, 6 and 7 at home or playing games 3, 4 and 5 at home. The format for the Stanley Cup Final remained 2-2-1-1-1.
1998-99 - The NHL's clubs were re-aligned into two conferences each consisting of three divisions. The number of teams qualifying for the Stanley Cup Playoffs remained unchanged at 16.
First-round playoff berths were awarded to the first-place team in each division as well as to the next five best teams based on regular-season point totals in each conference. The three division winners in each conference were seeded first through third for the playoffs and the next five best teams, in order of points, were seeded fourth through eighth. In each conference, the team seeded #1 played #8; #2 vs. #7; #3 vs. #6; and #4 vs. #5 in the quarterfinal round. Home-ice in the Conference Quarterfinals was granted to those teams seeded first through fourth in each conference.
2010-11 - New tie-breaking procedure: In the event two or more clubs are tied in points at the conclusion of the regular season, the standing of the clubs in each conference will be determined in the following order:
1. The greater number of games won excluding games won in the
Shootout (NEW for 2010-11).
2. The greater number of points earned in games between the tied
clubs. If two clubs are tied, and have not played an equal number of
home games against each other, points earned in the first game
played in the city that had the extra game shall not be included. If
more than two clubs are tied, the higher percentage of available
points earned in games among those clubs (and not including
any“odd” games) shall be used to determine the standing.
3. The greater differential between goals for and against for the entire
In the Conference Semifinals and Conference Finals, teams were re-seeded according to the same criteria as the Conference Quarterfinals. Higher seeded teams gained home-ice advantage.
Home-ice advantage for the Stanley Cup Finals to be determined by points.
All series remain best-of-seven.
-- Playoff statistics and information courtesy of NHL Official Guide & Record Book and Total Hockey