Mahjong Strategy: Push or Fold 4 part 1 / Maximizing Game EV

Mahjong Strategy

Hi all ! Thank you for checking this website ! This article is on Push or Fold judgement considering game EV, not round EV. Previous articles have been based on my Tenhou logs, but this article is a summary and translation of Unimaru’s video on Youtube. To write this article, I got approval from him. Thank you, Unimaru san ! You can watch his video from the link below.


As some of you may know, Unimaru is one of the most famous Japanese Mahjong Youtubers whose target audience are intermediate to advanced players (Tenhou 5-7 Dan). Well, let’s get started !

First 38 seconds are about point system on Tenhou. He seems to be 7 dan now, but got to be 9 dan 4 times.

After that he explains the situation. East 2 and it is a flat point situation, the player on the right Riichi-ed and Unimaru has 7,700 Ryanmen Tenpai. Just drew 4p. Push or Fold ?

He counted Suji which may hit to the Riichi of the player on the right. There are just 4 Suji live: 14m, 14p, 36p, 25s.

From 1:00 he explains steps to judge Push or Fold, which are

  1. estimate deal in percentage
  2. calculate round EV
  3. calculate required point to push (this is round optimal)
  4. consider winning value index (explain it later) to calculate game optimal required point to push.

From 1:26, he explains EV will be largely affected by deal in percentage of the tile to discard. To estimate deal in percentage, we should count Suji which didn’t hit. Alreadly 14 Suji are dead, and 7p is safe tile. In this case, deal in percentage of 4p is 18% usually, and we should add 2-3% because 5p is discarded before RIichi. So deal in percentage is around 20% (Actually, I couldn’t find this data on Miinin’s book, but 20-25% will be reasonable).

From 3:49, he explains round EV which is showed on Miinin’s book. The situation is we have 7,700 hand with Ryanmen Tenpai, play against Ko: non-dealer Riichi, 14th turn.

In this case, if we discard 0% hitting tile and still try to win, our EV is 2,500. and if 10% hitting tile, our EV is 1,700. So if hitting probability increase by 10%, EV decrease by 800, because Miinin mentioned the relation ship btw these 2 numbers is linear. Now we try to discard 20% hitting tile, so EV will be 1,700-800=900.

We should compare this 900 to the EV when we Betaori: discarding only safe tiles and giving up winng , which is -1,100 for non dealer. Obviously 900 is larger than -1,100, so we can push this 4p by a large margin.

Phew, this already got to be the longest article in this website, but still half way to go. To be continued !