@artsyhonker For me it works like that: every month i sum up the money i have that month, and substract my recurring costs like rent, insurance, telephone bill etc and the rest is a sum I write down in a table and everytime i spend some money I write that down in that table, and the new total of what is still left.

If I'm short on money I will calculate how much money I have per day and then try to stay under that.