With thanks to Cedric Dahl for this excellent video, I recommend everyone watches this.
'How to calculate your Live to Work Ratio: Step 1: (annual income after taxes) - (annual living expenses) - (total debt) -- take this number, and...
Step 2: Divide by annual living expenses.
You'll be left with a decimal -- this represents how much of one year you can take off, for every year that you work. '