Iishanten (One Away) - One Tile from Tenpai

What is Iishanten?

Iishanten means being one tile away from tenpai in mahjong. With a shanten count of 1, drawing one useful tile puts you in tenpai. The shape and tile acceptance of your iishanten greatly affects subsequent development, making it a crucial stage.

“Shanten” indicates how many tiles you need to reach tenpai/win.

Basic Shapes

Shape Type	Description	Example
Two ryanmen	Widest acceptance	23m 45p
Ryanmen + gukei	Balanced	23m 12p
Two pairs	Future potential	11m 55p
Block overflow	5 blocks	Requires selection

Shanten Counting

Winning hand: 4 melds + 1 pair = 0 shanten (tenpai)
1-shanten: 1 more tile = tenpai
2-shanten: 2 more tiles = tenpai
3-shanten: 3 more tiles = tenpai

Tile Acceptance Numbers

Good iishanten:
- Two ryanmen: 16 tiles
- Ryanmen + kanchan: 12 tiles
- Ryanmen + penchan: 12 tiles

Bad iishanten:
- Two kanchan: 8 tiles
- Two penchan: 8 tiles
- Pairs only: 6 or fewer

Strategy by Shape

Good Iishanten

Situation	Recommendation	Reason
Good shape	Push forward	Wide acceptance
Bad shape	Consider reshaping	Poor efficiency
High value confirmed	Proceed as-is	Good return
Late game	Consider folding	Running out of time

Shape Improvement

1. Taatsu selection
   - Prioritize ryanmen
   - Discard gukei

2. 5-block handling
   - Cut weakest part
   - Maximize acceptance

3. Pair usage
   - Pon to tenpai
   - Ankou potential

4. Yaku consideration
   - Secure yaku
   - Consider value

Good vs Bad Iishanten

Good Iishanten Types

Shape	Acceptance	Feature
4-connected	Up to 20	Like 2345
Extended ryanmen	~16	Like 1134
Nobetan	16	Like 1234
Complex	12-16	Various

Bad Iishanten Types

Shapes to improve:
1. Multiple isolated pairs
2. Edge-heavy gukei
3. Honor pairs only
4. Gukei without dora

From Iishanten to Tenpai

Method	Content	Advantage
Self-draw	Draw useful tile	Most basic
Calling	Pon/Chi	Speed priority
Reshaping	Change direction	Improve acceptance
Folding	Switch to defense	Avoid loss

Calling Decisions

When to call:
1. Late-game push
2. Yaku confirmed
3. Stopping opponent
4. Dealer renchan hunt

When not to call:
1. Cheap hand
2. Riichi has high value
3. Still early
4. Want defense options

Tenpai Probability

Turn	Good Shape	Bad Shape
Turn 6	~70%	~40%
Turn 9	~60%	~30%
Turn 12	~45%	~20%
Turn 15	~25%	~10%

Expected Turns by Acceptance

16 tiles: ~4 turns to tenpai
12 tiles: ~5.5 turns to tenpai
8 tiles: ~8 turns to tenpai
4 tiles: ~16 turns to tenpai

Push/Fold Decisions

Factor	Push	Fold
Value	Mangan+	1,000 pts
Shape	Good	Bad
Turn	Early-mid	Late
Score	Behind	Leading

Risk Management

Risk management:
1. Keep genbutsu
2. Mind suji
3. Safer tiles first
4. Avoid ippatsu

Common Mistakes

Miscounting shanten
- Practice accuracy
- Watch 5-block hands
Miscounting acceptance
- Consider used tiles
- Calculate precisely
Missing shapes
- Multi-wait potential
- Don’t miss changes
Premature riichi
- Can’t riichi iishanten
- Confirm tenpai

Advanced Techniques

Iishanten maintenance
- Delay tenpai intentionally
- Wait for shape change
Transition to multi-wait
- Iishanten to 3-way wait
- Maximize acceptance
Late yaku addition
- Add yaku at iishanten
- Improve value

Tenpai: One away from winning
Shanten-suu: Distance to tenpai
Ryanmen: Two-sided wait
Gukei: Bad shape wait
Uke-ire: Tile acceptance

Summary

Iishanten is being one tile away from tenpai - a crucial stage where shape and acceptance greatly affect your game. Push forward with good shapes, consider reshaping with bad ones. Beginners should first learn accurate shanten counting, then develop acceptance-conscious hand building. Good iishanten decisions improve your tenpai rate and lead to more efficient mahjong.