I tried to throw together a simulation in CADD but couldn't get it to work, so I went with this. I think it works.
All chains are going to stretch, that is unavoidable. You may notice it when you're riding down the road and your chain randomly starts slapping your chainstay. That's one indication. Unfortunately, chains can only stretch so far before they start causing damage because of their stretch, and need to be replaced. Most shops will have a chain stretch checking tool (Stretch/wear gauge), and more than likely they'll check your chain in a matter of seconds free of charge.
Another general rule to keep in mind is, if you ride a lot, every year. If you ride near every day that you can, you grind, you do sprocket stalls and grinds, your chain might not last a year, but if it does, replace it. There are very few chains I can think of that I would keep after a year. Probably the only one is the 1G8, the chain on steroids.
Another general rule to keep in mind is, if you ride a lot, every year. If you ride near every day that you can, you grind, you do sprocket stalls and grinds, your chain might not last a year, but if it does, replace it. There are very few chains I can think of that I would keep after a year. Probably the only one is the 1G8, the chain on steroids.