Basically you need to divide your entire gambling into two categories: 1. Gambling for fun 2. Gambling for profits.

For fun gambling, I guess you must spend zero from your earning as these days you will be somehow able to get free credits to gamble. Hence, it will not be a wise idea to spend for fun seeking gambling.

For making profits from sportsbetting or any other profitable gambling, I guess you may spend up to 2% of your earning. Because, you may get some returns from your this type of gambling and based on your performance you may increase or decrease your amount of money to gamble. If you are not able to make any profits then you must completely switch over to fun seeking gambling.