Kan

Kan has some special rules applied to it. A kan is a quad, which is four tiles of the same kind (in the same suit), that is revealed in order to draw a supplemental tile. A kan has a two-fold advantage: a player is guaranteed to have all of one kind of tile, as there are only 4 of each kind, and if a player chooses, the option of calling kan is available.

Tiles that constitute a kan are generally treated as 3 tiles (triplet) plus 1 extra. The tile claimed by kan is an "extra tile". By calling kan, a player has the right to draw from the dead wall and increase the number of dora indicators. This extra draw allows a player to retain the ability to complete a hand. The maximum number of kans called in any hand is 4, with exception of 5 in the case of the previous 4 are all called by one player in the attempt of the Suu Kantsu (Four Kans) yakuman.

Unlike a run or a triplet, a quad is not a legal meld until it is called or declared and a supplemental tile is drawn. Unless part of another meld, the 4th tile functions as an "extra tile". Therefore, a quad must be split up in order to win. Likewise, the Japanese include the term kan in melds formed by kan calls, but do not so with chii and pon. A chii call yields a minjun. A pon call yields an minkou. A kan calls yield a daiminkan. Furthermore, a declaration of a kan yields a shouminkan (chakan) or an ankan.

Daiminkan
A daiminkan is considered as an open kan. When a player has ankou (closed triplet), then the player may claim the 4th tile when it is discarded.

Chakan
Chakan describes a situation where player upgrades a minkou (open triplet) to a kantsu. A player may have called pon to produce an open triplet. During the course of a hand, a player may also end up drawing or possessing the 4th tile. A player may call kan to add the tile to the pon. The 4th tile gets added on top of the tile marked sideways on the pon.

If a player had made a pon and the 4th tile is discarded, then the player cannot call kan to add the tile to the pon.

Ankan
For the ankan, a player may have all 4 of one type of tile in the hand. After the player's draw, a player may call kan before discarding. The closed kan is limited to the player's turn. After showing all four tiles to the table, the player may set the kan to the side as indicated in the example. If the hand is closed before making the closed kan, then the hand remains closed, despite making the kan call. Therefore, a play like riichi is still applicable, until an open call is made later on.

Chankan
Chankan is the yaku for "robbing a quad". Limited to the added kan and one instance of the closed kan, a player in tenpai waiting for a tile applied to a kan may "steal" the tile and claim it as a winning tile. For added kan, it can be any hand in tenpai, in which three of one type of tile is already used in a minkou. For closed kan, this is limited to a tenpai Kokushi Musō.

Rinshan kaihou
Rinshan kaihō is a yaku where players win by tsumo from the dead wall. Naturally, a player must be in tenpai after a kan call.

Rinshan pao
This is a modified rule to rinshan kaihō. For this rule, if a person discards a tile and a player calls a daiminkan, a rinshan tsumo would be deemed equivalent to that of a ron. In order word, the player who discards the tile for the daiminkan is fully responsible.

Setting up rinshan
A hand with a kan available, either by chakan or ankan, may have an extra tile in the hand. Namely, that is the 4th tile to an existing minkou or ankou. Of course, this may not be the case if the tile applies to a meld that uses that one tile. In general, the 4th tile functions as an extra tile; and therefore, tenpai is achieved via a drawn tile. Until that happens, it is recommended to hold off calling kan.

Fourth tile used in an existing meld:

Currently, this hand is in tenpai for or. It contains an ankan of four. However, one of the tiles is used for a shuntsu, forming two distinct melds:  and. In this case, it may be disadvantageous to call kan, as it could break tenpai. Tenpai could still be retained if a, , or is drawn.

Same hand, but a 6-sou is drawn:
 * Draw:

For the same example hand, now a is drawn; this tile completes a new meld of. Therefore, a kan can be called in this instance without breaking tenpai, by which, a dead wall draw of or  would qualify the hand for rinshan kaihō. While this yaku is by no means guaranteed, at least, there is a chance for that yaku upon calling kan.

Limits on kan
Finally, two rules apply to kan, which limits a player's ability to make the call.

Per rules on the abortive draw, a game can only have a total of four kan calls. One exception allows 5 calls for kan, in which a single player had declared all of the previous four kan calls. The exception allows a chance for the rare suu kansu yakuman.

Per the rules on rīchi itself, a player may call kan for an ankan, which is the only possible kan allowable after rīchi is declared. However, this is limited only if the call does not affect the original waits. Failure to account this rule results in chombo. In addition, players after calling rīchi may not call a daiminkan, as that would open the hand; but chombo is not applied here, as the call would simply not be allowed.