Here's one way to do it for say a month's period of time.

Working Money = Winnings - Taxes - Average Bills/Cost of Living

Then break Working Money up into parts for savings/emergency fund, extra spending money, and bankroll padding.

Edit: I'll go a step further.

Say you play $100nl for 25k hands/week (about 30 hours/week 16-tabling which is about standard for full ring) at 2 ptbb/100 and that there's only 28 days in a month for simplicity. In a month you'll make about $4000. Now we add in rakeback or bonuses or whatever benefits you get from whatever site you're on. We'll round this down to about $1500, so your income for the month is about $5500.

About $1500 or so will go to taxes depending on your state income tax and what you deduct and whatever else (assuming you live in the United States). That leaves $4000 to deal with. Now suppose your cost of living is $2000 for the month. That leaves you with $2000 to divide up however you like.