Make sure you do a lot of research before you decide to get into breeding your geckos! You must
be positive that you have a back-up plan in place in case you run out of room to keep all of your hatchlings.
Gecko babies are not as easy to "get rid of" as kittens or puppies - many animal shelters will not take them,
and many pet stores are not allowed to buy stock outside of their predetermined sources.
Read up on how to become a reptile seller or trader if that is your goal!
It is also a breeder's job to think about the ramifications of their breeding projects. If you own a sub-par or even defective gecko (perhaps your gecko's crests are very small, or it is missing crests due to genetic issues), I recommend that you think twice about breeding that animal. It can still be a wonderful pet, but think twice about allowing it to breed. The gene pool in captivity is regulated entirely by you and your fellow breeders - as long as we are "playing God" with their genetics, we should be mindful of possible outcomes. Would you want to buy a sub-par gecko for a future breeding project? If you wouldn't, why would anybody else? Make sure that any geckos you plan to breed are healthy and excellent representatives of their species.
Ideally, a female gecko should weigh no less than 35 grams before being introduced to a male for breeding. The male should be around the same size as the female, though in many cases a size difference has not caused problems during breeding.
Sometimes a male and female might seem uninterested in each other, but often, mating takes place at night when
you're sleeping. During copulation, a male will grab the female by her crests with his mouth and will
make contact to her vent with one of his hemipenes. You may hear some "squeaking" sounds as they vocalize to
each other. This act looks rough, and sometimes a gecko may receive bite-marks from mating, but they
generally heal well if the enclosure is kept clean.
About thirty days after successful copulation, a female will look to lay two eggs in a soft substrate.
If you are making use of a paper towel or similar substrate, you will want to provide the female with an
egg-laying box. (Honestly, it's a good idea to provide a lay box for any adult female, as they can lay infertile
eggs as well, and the box gives the gecko a comfortable enclosed space to dig and lay.) I prefer to use a wide Gladware-type container with many ventilation holes and a
little "hatch" for the female to crawl into. You can use many different kinds of substrate, though I prefer a
very slightly moist peat moss (if it still clumps together a lot, it is too wet - "just right" feels damp but still fluffy). The female will often taste the substrate
to make sure it's good enough for her eggs. She may spend all night digging and burying herself and the eggs in the
substrate.
I have read several sources advising to stay away from coco fiber/coir as a laybox and incubator substrate. At best, the material may stain the eggs, and it is thought that there may be a chance that the materials may leech into the eggs and harm them. I have not experimented with coir, so I cannot confirm or deny this claim, but I prefer to play it safe.
After eggs are laid, you may notice that your female has a bit of a "deflated" look, so that is something else to keep an eye out for if you're unsure if your gecko is gravid (carrying eggs).
A healthy female will lay a clutch of two eggs every thirty days or so. Viable eggs will generally look bright white all around (though if your eggs come out looking a little yellowish, it's recommended that you don't throw them out unless you're 100% sure they're infertile). Eggs can be incubated in a separate container; I prefer to use perlite as an incubation material. The perlite should be moistened, but then squeezed as hard as you can to remove all excess moisture before being added into the container. The eggs can be laid so they are only one-third submerged beneath the incubation material. An incubation cup can have tiny holes punched into it to provide air for the eggs and eventual hatchlings, or, if you prefer, you can try it without the holes and just open the lid once a week to vent in new air. Just be wary of checking the container often once you know incubation time is nearing an end, so you can catch hatchlings and make sure they have enough air.
Important: Do not rotate the eggs when moving them from the laying substrate to the incubator, or at any other
time. You can prevent this by making a small pencil mark gently on the top surface of the egg.
Incubation can go from around 65 days at room temperature, to all the way up to 120 days and beyond. If you
keep your home on the cooler side, your eggs may take longer to hatch, but this is thought to be beneficial to
the growing embryo, as it has time to absorb all of the egg's nutrients and may be stronger when it does finally
hatch.
You can check to see if your eggs are viable by "candling" them. Take the egg into a dark room and hold
it up to a very bright LED-type light (I use a mini book-light). If you see a small red circle at the top
of the egg, chances are, the egg is good. This red circle will develop quickly as the first week goes on,
so if you didn't see anything the first day, try again in a few days. Keep in mind that the less you handle
the eggs, the better (if for no other reason than to avoid accidents), so taking them out every day to candle them isn't a great idea. 
Generally, the two eggs in a clutch may hatch within an hour to within a day of each other. However, it is
not unheard of for a clutch to hatch around a week apart.
Please note, often first-time laying females have poorly calcified eggs, or they only lay one egg instead of two. As long as she is around 35 grams, is feeding well, and shows no signs of illness, this should not be a huge concern. Usually a healthy gecko will get it "right" around her second or third clutch.
One problem to be aware of before attempting breeding is egg-binding, or your gecko becoming unable to
pass eggs. If a female does not find a suitable laying place, or there are other health issues present
including a problem with calcium or D3, she may retain the eggs. The eggs may continue to grow and possibly
fuse together inside of the female's body, making it difficult or impossible for the eggs to be passed.
If your breeding female's sides start looking bloated, or she becomes very lethargic and ceases or slows
in food consumption, keep a close eye on her (but do not bother her overly much, as that can stress her
out even more and prevent laying attempts). If you are expecting eggs and they are very long in coming, it
may be worth your time to get your female X-rayed at a veterinarian's office to find out if the eggs can
be safely passed.
When hatchlings come out of the egg, they may stick their heads out and just rest for a while. Just let them
come out on their own! They may take a few minutes or around an hour to fully emerge. Once they come out, be careful, as they
can move very quickly. I like to keep two hatchlings of the same size in a small Kritter Keeper-type enclosure,
with a very small bamboo branch and fake foliage. Their water and food dishes should be very shallow to prevent
drowning, and their enclosure should be misted gently both in the morning and at night. Other than that, their
care is similar to an adult crested gecko.
A female gecko should be encouraged to take a break from breeding for a few consecutive months every year. One mating
with a male can cause a female to lay fertile eggs for several months (they can store sperm), so if you want
your female to stop laying, you may try a few different things. You may remove the male from her enclosure,
attempt to bring the temperatures
down to the high 60's, reduce the length of time your geckos receive light during the day, or a combination of
these.
The cooler weather and shorter photo-period will generally cause the gecko to stop laying eggs.
Most breeders use the winter time when temperatures are naturally chillier to "cool" their geckos. During the
cooling period, a female can rebuild stores of fat and calcium, and make her ready and healthy to go for
the next season.
Crested gecko genetics are still being figured out; one may cross a dalmatian-spotted gecko with another
dalmatian and their offspring might turn out to be a tiger-striped individual with few or no spots at all. It's exciting to see what your breeding
pairs return!
