How Koi-Koi scoring works

The formula in four steps

Here is one round, counted step by step: you make Tsukimi de ippai (5 points), call Koi-Koi (also written koikoi), later take the Curtain for Hanami de ippai as well, and stop with Shōbu (plain spelling: Shobu). Each step shows this game’s rule and Nintendo’s.

In a game you do not have to count: when you form a yaku, the Koi-Koi or Shōbu window shows what Shōbu would pay now, line by line (the yaku points, each multiplier with its reason, the cap, and the payment), and the end of the round shows the same count.

Step 1 in detail: which yaku count

Add every yaku in the winner’s captures, each with its extra cards: Inoshikachō with two more animals is 7, not 5. Only one light yaku counts at a time, and Chōfuku takes the place of Akatan and Aotan; everything else adds up, and one card may count for several yaku. The yaku page lists every value and combination.

Step 2: doubling at 8 points

In this game a base of 8 points or more is doubled (see doubling). It is a setting of each room, “Double at 8+ points”, and of the practice game against the computer; it is on unless whoever sets up the game turns it off. With it off, a round is multiplied only by its Koi-Koi calls. The table below shows a round with no Koi-Koi calls.

Step 3: the Koi-Koi multiplier

Every Koi-Koi call in the round raises one shared multiplier by one, whoever makes it: ×2 after the first call, ×3 after the second, and so on. It applies to whoever wins the round, so your own calls raise your own reward as well as your opponent’s. It starts again at ×1 every round. Calls are not limited: you may call again each time your total rises, and so may your opponent.

What this means for play, when to call and when to stop, is on the strategy page.

Step 4: who pays, and how much

Both players start the match with 25 points. The round’s loser pays its score to the winner, capped at what they have left: 40 points against a loser with 25 is a payment of 25. A player with no points left loses at once; otherwise the match ends after its last round (6 or 12, chosen when the game is set up), the player with more points wins, and equal points make a drawn match. Some Japanese rule pages count in mon (文), the traditional unit; this game says points.

This game and Nintendo side by side

All of the differences, including the ones outside scoring, are collected on the house rules page.

Ten worked examples

Each example was checked against the game’s own scoring code. The loser has 25 points unless the example says otherwise, and the doubling setting is on.

Points calculator

Choose the winner’s yaku, the cards they captured of each kind and the Koi-Koi calls, and the calculator shows the count. It starts on this game’s rules; “Nintendo’s rules” switches the doubling, the multiplier and the counting of Tane, Tan and the Sake cup to Nintendo’s, and removes the 25-point cap. With this game’s rules it gives the same result as the game.

The calculator needs JavaScript. The worked examples above show the same arithmetic, step by step.

The dealt hands, Teshi and Kuttsuki, are left out: they always score 6 on their own, with nothing to multiply.

Rounds that score differently

• Nobody calls Shōbu. When both hands run out, the round is drawn and nobody pays, even if someone holds yaku or has called Koi-Koi without improving since. The same player deals again.
• A dealt hand yaku (Teshi or Kuttsuki) ends the round at once for 6 points, as in example 10. The player who had it deals next.
• The last turn. When both hands are empty, a new yaku can only be scored with Shōbu: Koi-Koi is not offered.
• After a Koi-Koi, you can stop again only when your total rises, from a new yaku or one more card for a +1 yaku. If it never rises and your opponent never scores, the round is drawn.

The rules page covers the whole turn, from the deal to the Koi-Koi decision.