Go by the money you need not by the money you have, you see what I am saying. 

First calculate how much you need? 
Gas- 
Rent- 
Phone bills- 
internet - 
restaurants - 
Groceries - 

for me it is 1800 but I set aside 2000. I have 2 different bank account where my pay check goes. so  2000 goes to one and the rest goes to the other account. I never touch the other bank account, +/- I manage with the 2000. 

It works for me, I am not sure if it will work for you.