I mostly follow a 90- day calving season, starting about November 1. There are a number of reasons why. I've stated them here before, but I'm just relaxing in my recliner watching the Astros, so I don't mind doing it again. First, I have the defined season mostly because I only want to vaccinate, castrate, and wean once a year. There are many reasons for me choosing late fall / early winter.
1. Winters here are mild, so weather isn't the same issue for me that it would be for folks up north.
2. I have a dependable supply of inexpensive hay, so I don't mind the extra hay needed versus feeding dry cows.
3. My bulls aren't working in the summer heat like they would be if I calved in spring.
4. While I'd never say it's true every year, quite often the prices will start to drop in September, so I catch the top of the market in late July or early August.
5. It's often dry and always hot in July and August, so if the pastures are starting to suffer then the calves are ready to sell anyway, and I'm not having to sell them younger than I'd like to take the pressure off the grass.
6. While I do have a defined calving season, I don't pull my bulls. If a cow gets a few months behind then she'll likely work for someone else. They're usually worth quite a bit more bred than open. (I did pull my bulls when calving started for a year or two trying to prevent early calves, but then had trouble with neighbor bulls "helping out" so I gave up on that.
Someone mentioned record keeping earlier in this discussion. My father was an exceptional cattleman in many ways, but calved year round and didn't keep records until his last few years. I remember a number of times when we'd be riding through the pasture and he'd point out a good-sized calf, asking me "What do you think? Should I sell that calf?" I'd reply "How old is he?" Dad would reply that he didn't know. Then I'd say "Then I don't know if you should sell him yet." I wasn't being disrespectful when I gave that answer; I just didn't know what else to tell him.