Percentage of Income

I don't know about a formula for determining this...there probably is
one...but my father taught me to follow this rule of thumb --
rent/mortagage = 1 week's pay
utilites = 1 week's pay
food, medical, clothing, gifts, gas/travel = 1 week's pay
entertainment, savings, car payment, insurance = 1 week's pay
anything left over from any of the first three expenditures should be

put in savings even if you regularly save money in an account each
month. this way if you ever have an emergency there is 'extra' that's
been set aside.