Ippatus

What is Ippatsu in Japanese Mahjong?

Ippatsu is a special bonus yaku in Japanese Riichi Mahjong that adds one additional han to your hand if you win immediately after declaring Riichi, before any interrupting calls (chow, pung, kong) are made. Ippatsu is a one-han bonus that rewards swift victories immediately following a Riichi declaration. It underscores the drama of Riichi Mahjong: a tense moment in which opponents scramble to deny your “one-shot” chance. If you successfully win within that narrow window—before any calls interrupt the flow—your hand gains an extra han, often leading to substantial point gains.

How to Achieve Ippatsu？

Riichi Declaration：Ippatsu can only occur if you have declared Riichi.

Immediate Win Within One Turn Cycle：After your Riichi declaration, you must win either: On your next self-draw (tsumo), or On another player’s discard before any other player performs a chow, pung, or kong. If another player calls a tile (for chow/pung/kong) before you win, the possibility of Ippatsu is lost.

Adds One Han: If you satisfy the condition above, Ippatsu grants +1 han to your final hand score on top of Riichi and any other yaku or dora you may have.

What is the Strategy and Risk of Declaring Ippatsu?

Risk and Reward：Declaring Riichi locks your hand, but it enables both Ippatsu and Ura Dora possibilities. Landing Ippatsu is especially rewarding since it adds a free extra han without additional structural requirements to your hand.

Timing: Some players may delay Riichi by a turn or two to potentially improve their wait, but by delaying, you risk losing the Ippatsu window altogether. Conversely, declaring Riichi quickly maximizes your chance for Ippatsu but reduces flexibility in your hand.

Opponents’ Defense: Once you Riichi, expect other players to consider defensive play. Your opponents may call any tile to prevent you from drawing or claiming a winning tile uninterrupted.

Synergies: Ippatsu naturally stacks with:

• Riichi (1 han)
• Fully Concealed Hands if you win by self-draw (1 han)
• Other yaku such as Pinfu, All Simples, etc.

These combinations can rapidly escalate a hand from modest to high-value.