I originally typed this up in response to another thread but thought I'd just start a new one...
One way to tell if your snake is starting to get a little porky is if you pick him up and can feel a layer of fat under his skin/scales. I have a yellow belly who was generally the one who would get leftovers if someone else refused to eat. I eventually noticed that I could actually feel a more than normal layer of fat on her. If you experience it, it's very apparent.
Another thing to look for are the ends of their tales. I noticed this same yb started to get a kind of stumpy tail, unlike the normal tapered thin tail...I kind of attribute this to her growing too fast...
Here's the yb's tail...
As opposed to my spider and butter...
They're all roughly the same age, but the yb was always the better feeder...obviously...
I cut down her feeding schedule and her fat layer seemed to dissipate to a normal level...she went on a brief fast last year which helped as well...
Out of my three females I bred last year, she's the only one who didn't give me eggs. I definitely attribute this to her being too heavy. It was a lesson learned...
If you're going to feed on a heavier than normal scale you need to be more in tune with your animals...If you want to keep it simple, stick to a 5-7 day schedule...unless you're feeding prey items that are way too big, you'll never need to worry about your snake getting fat...
This is all my personal experience...there are a lot of experts here with tons more experience than I.
If they have any info, experience or thoughts please chime in!!!