If we spend more than 20 percent on gambling on a monthly basis then I think it is not in entertainment level. Because if a person invests 20 or 30 percent in gambling then he will definitely express his desire to make more profit from it. Which in turn may lead him to loss rather than gain. And if 10 to 15 percent is used it is definitely acceptable. A gambler will have big financial problems when he spends more money. At some point he decides to manage his gambling by borrowing money to solve his crisis. Which in turn will lead him to a terrible situation.
The percentage amount will depend on each person and how willing they are to use their money to gamble. Maybe 20 percent is an amount that he can afford and is still reasonable for gambling, while others think that 20 percent is not a good idea for gambling every month. Well, there is no ideal limit for each gambler because they will use different percentages in gambling, so that is not a problem. As long as they can gamble responsibly and control themselves, 20 percent might be enough for them to gamble, and maybe they won't use the 20 percent but under 20 percent. But if he decides to borrow money to gamble, that is not recommended because it will cause more problems for him. He should take care of himself while gambling so as not to use much money.