I've tried to do this for years but never been able to figure out how it works in practice. My wife and I have settled on just looking at our accounts every week and seeing that we have enough buffer, but I really feel like there is some skill that is missing.
It wasn't until I really grokked YNAB's methodology[1] that I got out of the paycheck-to-paycheck cycle, saved up for an emergency fund, and begun seriously paying off school loans. Their 4 rules and their app have changed my financial life. Like atarian said, having a budget really does free you.
I don't know if I have ever really lived paycheque to paycheque though. I've pretty much always been in the situation where I was able to cover a surprise $500 expense. My level of spare cash has fluctuated pretty wildly from $500 to $3,000 though and my long-term savings should be higher.
