Kan
Kan is a special tile call in the game. This call forms a meld from four identical tiles. While appearing as a four-of-a-kind, a kan meld actually functions as three-of-a-kind plus one extra. With this in mind, upon calling kan, players are required to make an extra draw of the dead wall. This drawn tile is called the rinshanpai.
Procedure
Like the other tile calls, kan is also a tile call. However, it comes with special properties and rules. These rules apply when a player possesses or gains possession of four of the same tile; and then the player makes the kan call.
- The player calls "kan".
- They set aside the four identical tiles next to any open melds. The four tiles now count as one meld.
- They draw a replacement tile from the dead wall to maintain the proper hand size for four melds and a pair.
- The last tile from the wall is added to the dead wall, so that the dead wall contains 14 tiles at all times. Some players omit this step and just end the game when a total of 14 tiles remains in the wall and the dead wall combined.
- The player flips the next dora indicator. Some rules may have this step last depending on the type of kan declared.
- The player may declare a win, declare more kans, or end their turn by discarding normally.
Kan types
Kan can occur under three different occasions; and thus, there are three types of kan.
Daiminkan
This is also called an "open kan". A player possesses three of a tile type. Then the fourth is discarded. The player may claim the discarded tile and form a daiminkan. Upon doing so, the player has opened the hand.
Most rules do not allow to flip the kan dora indicator immediately after a daiminkan declaration. It is usually flipped after discarding, or upon another kan declaration on the same turn. Some rules allow the kan dora indicator to be flipped immediately.
A daiminkan may not be made with the last discard of the game, which invokes the follow up procedure to take a rinshanpai. Because all tiles from the regular wall are used, no replacement tile from the regular wall to the dead wall could be made in order to maintain the dead wall at 14 tiles. Taking a rinshanpai in this case would reduce the dead wall count to 13, which not acceptable.
Shominkan
Also referred as an "added kan", a player had previously called pon to form a minkou, or open triplet. Upon drawing the fourth tile, the player may add that tile to the minkou and upgrade it to a shominkan or chakan. If the fourth tile was discarded by another player, it cannot be claimed by kan. The kan dora indicator is flipped at the same time as for a daiminkan.
The player may declare this kan during any turn; and therefore, the player does not need to declare kan immediately at first opportunity. If the player has just claimed a discarded tile instead of drawing a tile from the wall or the dead wall, then the ability to declare kan is disabled on this turn. The player would have to wait for the next tile draw instead. It is also forbidden to declare a kan while the wall is empty, because the dead wall cannot be replenished.
If another player is tenpai and the added tile completes his hand, that player may call ron immediately after the shominkan declaration. This is called chankan or robbing the kan. It ends the hand before the kan is completed, therefore no kan dora indicator is flipped.
Ankan
Also known as a "closed kan", a player may draw all four of a tile type. Unlike the other two kan types, ankan keeps the hand closed. That's despite the declaration to the other players and the revealing of the four tiles. The kan dora indicator is flipped immediately.
Like a shominkan, an ankan may be declared on any turn while the player holds all four tiles. The same restrictions as for the shominkan apply. An ankan may not be subject to chankan, except against a kokushi tenpai.
Multiple kan calls
If in possession with the proper tiles, a player may call kan more than once consecutively. This is physically possible, but extremely rare, up to four consecutive times.
Example:
Draw:
In this example, kan may be called twice in a row after drawing 
. Both the and 
may each be called for shominkan, before making a discard. Naturally, this must be done one at a time, following the proper procedure for kan.
Rinshan kaihou
Rinshan kaihou is a yaku gained by calling tsumo on the replacement tile after any type of kan declaration.
Chankan
Chankan is a yaku for calling ron against a shominkan declaration.