I'm outside the mold with my thinking. I never breed my mares back after they've foaled. I like to let them have the year off to raise their foals, recover their shape and musculature and just enjoy being a herd horse for that year. I MAY, if it's a really exceptional mare, breed her again when her foal turns to a yearling but many times I don't until it's even been 2 years. It keeps my mares healthy and happy and gives me lots of quality time with the foals for handling and training.
The only exception to this plan is the broodie with rare lines or who throws really exceptional foals who is getting older and coming to the end of her productive life. I may keep one of those mares in foal year after year until she's no longer able to settle or carry. If I have a daughter though, then I tend to retire my mares fairly early too.