Nearing the end of the month...

And it appears I've going over my budget again. I'm not sure what the issue is. I keep trying to readjust my budget, and I keep being just a little over it. Maybe the trick is to set my budget low so that when I go a little over it, it's actually not too much over?

Aggregating across the last four months, I am about $400 over my budget. Is my saving rate of 10% unrealistic? Should I be spending more/less? Does the 10% even mean anything if that's what I budget for, but I'm always over budget every month?