830. Drawing Lots

Shabbos 23:17

It is prohibited to draw lots or to play dice on Shabbos because doing so is tantamount to performing transactions. One may draw lots with the members of his family in order to determine who will receive which portion in order to avoid disputes.

Shabbos 23:18

It is prohibited on Shabbos to calculate accounts, both regarding concluded matters and upcoming matters; this is a preventive measure out of concern that one may come to write. Calculations that are not of practical application may be made on Shabbos, such as how much grain one had in a given year, how much money his son's wedding cost, etc. Since these matters have no useful purpose, there is no difference between making such calculations on Shabbos or during the week.