There are a few ways to tell if a hen is possibly or likely laying, though more often than not what you are looking for is signs that she is not laying. They are indications, not absolute proof.
When a hen is laying or getting ready to lay she probably has a bright red comb and wattles. If the comb and wattles are pink or orange, she is probably not laying. One problem with this is that different hens have different colors or shades for “Bright Red”. You kind of need to know what her natural color is. Also some hens can change comb and wattle colors on a short term basis for other reasons. Even with these limitations, it is a good indicator which ones might be laying.
You can look at the vent. A hen that is laying or getting ready to lay or just stopped laying will have a large moist vent. If the vent is small and dry she is not laying. A moist vent is not a guarantee she is laying, just that she is close. It also does not tell you about her frequency of laying. But a small dry vent means no she is not so maybe you can eliminate some.
The distance between pelvic bones is another indicator. The exact distance required will depend on the size and conformation of the hen, but a wide distance between pelvic bones means she is laying or at least close. Maybe you can get an idea by trying them all for comparison. Measure how many fingers fit.
I haven’t tried these but if you put some food coloring in the vent in the morning you will probably see streaks of color on any eggs that are laid. Those streaks might be fairly light but there have been a very few photos on here where this does work, at least some times. I’ve heard you can also do that with different colors of lipstick around the vent, but I’m not going to explain to my wife why I’m putting lipstick on a chicken’s vent, even if I’m not using her lipstick.
How badly do you really want to know? Get a surgical glove and a lubricant. After they are on the roosts at night stick your finger down the vent. You should be able to feel an egg in the shell gland if they are going to lay an egg the next day.
Weren’t ready for that last one were you? Have a nice day.
