Chankan

Conditions

• Another player must attempt to add a fourth tile to an existing open triplet (shouminkan / added kan) — this is sometimes called “upgrading a pon to a kan”
• The tile they are adding must be the tile you need to complete your winning hand
• You call ron on that tile, intercepting the kan before it is completed
• This only works against shouminkan (added kan) — you generally cannot chankan against a closed kan (ankan) or an open kan declared from a discard (daiminkan)
• Exception: Under some rule sets, you can chankan a closed kan if it would complete kokushi musou (thirteen orphans), but this is a rare edge case

Strategy Tips

• Chankan is one of the rarest yaku in the game. You cannot plan for it — it happens when an opponent tries to extend a pon into a kan using exactly the tile you need. When it happens to you, it feels like stealing a win out of thin air.
• Be aware of chankan as a risk when you’re the one making a shouminkan. If you’re adding a tile to an open triplet, that tile is briefly “exposed” and can be claimed by any tenpai player. In a dangerous late game, think twice before upgrading your melds.
• While you can’t aim for chankan, knowing it exists helps with defense. If an opponent is tenpai and you’re about to extend a pon, consider whether the tile you’re adding could be their winning tile. Sometimes it’s safer to skip the kan.