What is Chiitoitsu? How to Build and Score Calculation Explained for Beginners

What is Chiitoitsu?

Chiitoitsu (七対子) is a special yaku in mahjong where you have 7 different pairs (toitsu). While normal mahjong requires 4 sets + 1 pair, chiitoitsu is a special form where you win with 7 pairs. Also called “chiitoi” or “nikoniko.”

It requires unique hand building and has high defensive capabilities, making it a yaku worth actively aiming for depending on your starting hand.

Detailed Explanation of Chiitoitsu

Conditions for Chiitoitsu

Examples of Chiitoitsu Shapes

Valid chiitoitsu:

11m 33m 55p 77p 99s EE GG

Invalid examples:

Usage Examples

Real Game Situations

Example 1: Starting Hand Decisions

"5 pairs! Going for chiitoi"
"Toitoi or chiitoi, hard to decide"

Example 2: Hand Building Policy

"Cut isolated tiles for chiitoi straight"
"Iishanten but worried about duplicates"

Example 3: Winning Joy

"Chiitoi dora 3 for mangan!"
"Got riichi and one-point read for chiitoi"

How to Build Chiitoitsu

Basic Strategy

1. Aim when many pairs in starting hand

   • 4+ pairs is the guideline
   • 3 pairs is difficult

2. Cut isolated tiles first

   • Discard floating tiles
   • Sometimes break taatsu too

3. Watch for duplicates (4th tile)

   • Be careful of 3rd tile of same type
   • Drawing 4th tile breaks the shape

Chiitoitsu Process

Early: Count your pairs

Starting: 11m 33m 5p 77p 9s EE S WW N WW G
→ 5 pairs, chiitoi is promising

Mid: Cut isolated tiles

Cut 5p, 9s, S, N, G
Make new pairs from drawn tiles

Late: Wait shape

6 pairs + 1 isolated = tanki wait
Example: 11m 33m 55p 77p 99s EE W
→ Waiting on W

Related Terms

• Toitsu: 2 same tiles
• Toitoi: 4 triplet yaku
• Tanki Machi: Single tile wait
• Menzen: Closed hand state
• Ryanpeikou: Similar-looking yaku

Common Mistakes and Points to Note

Points Beginners Often Mistake

1. 4 Same Tiles Treatment

   • 1111m = 1 pair
   • Doesn’t count as 2 pairs

2. No Calling Allowed

   • Pon breaks chiitoitsu
   • Must build in menzen

3. Confusion with Ryanpeikou

   • 1122334455667 = ryanpeikou (not chiitoi)
   • Similar shape but different yaku

4. Choice vs Kokushi

   • When many terminal/honor pairs
   • Need to judge which to aim for

Chiitoitsu Scoring

Special Fu Calculation

Chiitoitsu is always calculated at 25 fu:

Point Reference Table

Chiitoitsu Tactics

When to Aim for Chiitoitsu

1. Many pairs in starting hand

   • 4+ pairs
   • Especially 5 pairs is promising

2. Want to play defensively

   • Pairs are relatively safe
   • Options remain until late

3. Irregular development

   • Normal hand hard to build
   • Have dora pair

Chiitoitsu Strengths and Weaknesses

Strengths:

• High defense (can cut isolated tiles)
• Dora easy to include (2 of 14 tiles used)
• Hard to read (special shape)
• Simple wait (tanki only)

Weaknesses:

• Can’t call (menzen only)
• Weak to duplicates (4th tile breaks it)
• Hard to increase score (base 2 han)
• Hard to riichi (tanki wait is hard to win)

Compatible and Incompatible Yaku

Compatible Yaku

Incompatible Yaku

• Pinfu: Requires ryanmen wait
• Tanyao: Theoretically possible but…
• Iipeikou/Ryanpeikou: Requires sequences
• Sanshoku/Ittsu: Requires sequences

Practical Tips

Hand Building Decisions

1. Decide direction early

   • Decide by turn 5-6
   • Avoid being half-hearted

2. Duplicate danger

   • Be careful of 3rd tile
   • Safe if 2 visible in discards

3. Riichi decisions

   • Tanki wait is hard to win
   • Damaten is also an option

Defending Against Chiitoitsu

• Reading tanki: Suji doesn’t work
• Non-genbutsu is dangerous: Any tile can hit
• Watch pair drops: Late pair discards may indicate chiitoi

Conclusion

Chiitoitsu is a special yaku with unique appeal, different from normal mahjong. The distinctive 7-pair shape can be very easy to build depending on starting hand, and has high defensive capabilities making it a practical yaku. Beginners should learn the three basics: “7 different pairs,” “4 same tiles = 1 pair,” and “menzen only.” When you see a starting hand with many pairs, don’t forget that chiitoitsu is an option.