A Yahtzee scores 50 points the first time that you get one if you place it in the yahtzee box in the lower section. If you have already scored a zero in that box then the 5 of a kind is no longer a yahtzee and scores the sum of the dice. Example, getting 5 sixes would score 30 in the 6's (upper section), or 3 of a Kind, 4 of a Kind, or in the Chance box.
Technically, you can score 13 yahtzees. But I've only seen four scored in any of the games that I have played with real people and only two with the dice monsters.
The max score you can get under perfect play is: 880 points possible inYahtzee with Buddies. 5 x 1, 5 x 2, 5 x 3, 5 x 4, 5 x 5, 5 x 6, 35 Bonus, 80, 80, 50, 50, 50, 50, 50.
The max score you can get under perfect play is: 880 points possible inYahtzee with Buddies. 5 x 1, 5 x 2, 5 x 3, 5 x 4, 5 x 5, 5 x 6, 35 Bonus, 80, 80, 50, 50, 50, 50, 50.
The second yahtzee can be played in any of the other open boxes meaning a box that you have not placed a zero in. In the upper section, the second yahtzee scores +50 and also the sum of the face value of the dice. So you might get from 55 (yahtzee of 1's) to all the way to the max of 80 (yahtzee of 6's).
There is an achievement where you don't want to score the yahtzee of all ones into the yahtzee box - Precision Fail achievement where you score the yahtzee in chance and score a zero in all the other boxes.