how much 'extra' do free range chickens need?

I'm sure they're not starving. Periodically pick a few randam birds up and feel the breast bone. I do offer free choice layer feed for my birds, even when they're out all day. They mostly eat it in the morning or evening though, so they go through very little feed. Now as fall comes on (don't know about your seasons there), they will begin eating more feed, because the bug population will die down, and the grass will start drying up/dieing. So supplementing is season dependent to a great extent.

 

Right now, my eight free-ranging chickens barely eat any of their laying pellets I put out for them. I expect they will come to depend on their feed to a greater and greater extent as the seasons change, and available 'wild' food slowly disappears...

 

My free ranging chickens are nice and fat and it's due to their free ranging. I do offer layer pellets which they snack on in the morning and evening (the only time their in the coop). And I occasionally throw them left overs from the kitchen.
Last year at this time I stressed over everything- their food, how much time they free range, etc. But, if you think back to 50 plus years ago, all chickens got was a few handfulls of scratch and they were left to their own accord. So, I leave mine to enjoy the "wild", and their eggs taste better than ever!! I wouldn't worry about it.

 

My only comment would be is to make sure that there is enough oyster shell for them.

My ladies free range all day, and I have made over the years made an oyster shell path to the door of the coop. It keeps the path neat and tidy and always has shell at thier disposal.

 

Mine free range all day every day. I put layer pellets in their coop when i let them out, but they don't stop to eat them. They just run like feral dogs to the porch where they know I feed the outdoor cats every morning. I give the cats time to eat for an hour then let the hens loose. The hens eat what is leftover then make a beeline to the front yard to search for morning bugs. I barely see them all day. They will eat the layer pellets as they return to roost for the night. In the winter they eat more. Just offer it to them and they will eat it if they want. Everything else is just junk food. They're like children sometimes. They'll devour what's not good for them and leave the nutrition for last.