The other folks in this thread have already given you some good input, and I can't add much to it. We wean our calves at around 6-7 months and they will typically average around 575-625 at that time. We started preconditioning our calves for 45 days before selling a few years back and found that it's worth the extra effort and expense to do so. I'm a small producer, so the local cattle alliance/feeder calf sales that are held several times a year helps us by getting enough head together for truckload lots that the buyers will pay more for at than the regular weekly sale. Sometimes you just have to sell them when you can, but if I have some calves to go to the weekly sale, I try to avoid selling in July and October. One of my older friends that trades cattle for a living told me years ago that, at least in our market, those are months to avoid selling calves if I can due to the prices going down some due to the heat in July and the temperature swings in October making the calves more likely to get sick. The market the last few years hasn't been as seasonably predictable with what prices will do, so it's hard to know for sure when is the best time. Usually the week before or after I sell mine is the best time. Ha ha.