Last year it was about 20% of net income due to a specific long range commute circumstance (220hrs). This year it should go back down to a customary 10-13% of net, based of a more common 60-70hr/yr mission profile, which I'll prob won't even meet this year, for I am airplaneless still. 15% of net is what I realistically have set for my household budget.
I do admit, if I didn't work professionally as a pilot I would be making some efforts to increase my allotted budget for flying. I get away with diluting a lot of my proficiency flying with the professional flying I do. So in essence my recurrent training is being subsidized by my day job. If that wasn't the case I would have to take steps to include more flying into the budget. 20% would be a more appropriate figure, otherwise it'd be less destination flying and that's just no fun.