Here's my one-question check to see if I've achieved work/life balance:
Can I do my dishes in peace without feeling a sense of urgency burning in the back of my mind?
If I can mindlessly (and slowly) do my dishes with no rush, no worries, and no 1000 miles/hr thought train going on in my brain, then I've achieved work/life balance.
Another thing to note: work/life balance can be temporary. This depends on the person; some people (like me) tend to work in ultra-productive bursts vs. others tend to work steadily over a long period of time.