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IMHO really rare, but then happened with several eggs from the same batch.
I used to live near an egg farm. A commercial supplier, but they had a little stand by the road where they did direct sales. They sold all the grades of eggs you don’t see in stores, by the flat. One of the options was double yolkers. Occasionally you’d find a triple.
You can tell before cracking the egg?
You can shine a light through the eggshell to see what’s inside. It’s called candling.
Double-yolkers are bigger and usually weirdly shaped in my experience. It's not a guarantee or anything, but they never seem to look like a normal egg
No but the thing is, they ONLY sell double yolkers. That way they don't have to check. It's double in every egg. Hmm?
I think some chickens are more likely to lay them than others (due to age, or genetics). After that the eggs are somewhat larger, and you can check by shining a light through it
We once had a larger than normal egg from a local source. When we opened it, it was a normal single yolk egg with a tiny otherwise fully formed shelled egg inside it. The tiny egg had a tiny single yolk.
I got that once when I had chickens. You get all kinds of weird stuff. Every once in awhile I'd get an egg without a shell. Just the contents in a membrane. Still intact usually.
Did you check the other yolk with a magnifying glass?
Nope, mixed it in for scrambled eggs. The small egg was about quail egg sized.
Meh, it can be selected for. My parents had double yolk eggs on the regular for years, until the only supplier in my corner of the country retired. Now we're stuck with boring single yolk eggs like everyone else ._.
I’ve gotten a few double-yolks from my chickens, mostly when they don’t lay for a day or two and pop out a really big one.
I got one with a spiral pattern in the shell the other day, like a streak of the wrong material got laid down during development or something. I’m not going to eat it, because I’m pretty sure it’s no good, but it’s cool.
And one of my quail that normally lays brown spotted eggs laid a completely white one last month.
Eggs are weird.
Some places sell cartons of eggs specifically branded as double-yolks.
https://www.homesteadeggs.com/product-page/double-yolk-carton
I think they tend to put them together. If I'm remembering correctly, it's a common practice to put similar eggs together rather than adding them to cartons at random, so consumers have more uniform cartons of eggs.
I had one carton a few months ago that was like 10 double -yolk eggs and ended up looking it up.
Yeo. They shine a light through the egg to see the double yolkers. You can buy packs of them.
Some slip through though
This happened many, many years ago as you can tell bythe quality of the image (almost certainly taken on a point and click, then scanned witha 10+ year old scanner) 
I've been looking at too many maps of china this week…
If you buy the XL eggs from the local farm shop, you've got a good chance to get some. I even got twins in all eight eggs once.
I once watched a guy who was working a Macca's kitchen with me manage to get 11 in a row when we were doing breakfast
supposedly its 1:1,000
If you buy “Jumbo” (US) eggs it’s not unusual to get multiple in a single pack.
I had like 8 in the last 2 dozen.
my parents once bought eggs from a guy on the side of the road claiming that they had 3 egg yolks. it was true. i wonder what the chickens could look like.
You must be yolking
I believe that some chickens are much more likely to produce them so it's not as unusual that if you find one to find another one in the same batch
I think it's related to the age of the hens, more common with the younger ones. Chances are there are others in the flock that are the same age, so that would make sense.
I find that it does seem to happen more often within one batch of eggs, vs different batches. Like if I get one double yolk in a carton, I'd at least not be that surprised if there's another in the same carton. Maybe it has to do with how they sort the eggs, idk
Happens regularly where I live, I think it's because the chicken was younger than usual?
My neighbor's had chickens and there were a couple who laid double yolks on the regular. They make the best scrambled eggs.
It is not rare naturally, so eggs like that are probably just sorted out on large farms
The way he explained it was, it's rare if the chicken doesn't usually lay them, but for some birds it's like 50/50.
I'm never sure how to feel about these. Is it a good thing? I feel like it's just extra cholesterol, and it throws off the regular yolk to egg white ratio. I almost feel like it's not a win.
Eating cholesterol isn't bad for cholesterol, saturated fats are what to avoid.
It's great if you can get one when baking. Recipes sometimes call for 1 whole egg and one extra egg yolk