There's lots of advice for managing your bankroll from a starting balance, but I don't have much in the way of an actual bankroll. What I do instead is set aside a monthly budget ($100) just for poker. It kinda works out like a $100 bankroll that resets every month - if I'm ahead, I cash out the winnings; if I'm behind, I put money in. If I bust, I'm done until the first of next month when I put a fresh $100 in.
I tried pretending it was a $1200 bankroll that I'm parceling out to myself over the course of a year, but that doesn't help the problem - it just changes the scale of it (that is, instead of "next month" I would look to "next year.) If I say that the bankroll is, in fact, $100, then would put me on $5 buy-ins, but my cash games typically run $10 - $40.
I find that I come out ahead more often than not, so I think my cash buy-ins are about right. I'm just starting to get serious about my poker game and track my performance.
I can figure out my win/loss rate over time with a spreadsheet, and my monthly budget puts a limit on my losses within a time frame. Is there a reason to come up with a number that represents my "total bankroll"? And if so, how should I calculate and manage that number?