The 4 Stages of a Dog Heat Cycle: Can You Spot the Signs?

Owning a female dog can be a challenge, especially if the pup is not spayed. All unspayed dogs go through an estrus cycle commonly known as heat. It’s during estrus that female dogs can become pregnant, so pet parents who don’t want to wind up with a litter of puppies need to know when their pups are going into heat and what to expect.

All-female dogs will go into heat for the first time when they reach puberty, which hits at around six months of age for most breeds. Each heat cycle brings about not just changes in fertility status but also changes in behavior. Dogs going into heat may urinate more often, pay more attention to male dogs, run away from their owners, or experience personality changes like becoming more affectionate or experiencing reduced or elevated energy levels.

These changes occur in four stages. Pet parents can read on to learn about each of them so they’ll know what to expect and how to protect and comfort their beloved animals during what can be a difficult time.

Stage One: Proestrus
Proestrus is the first stage of the heat cycle. It can last anywhere from three to 17 days, but most dogs spend around nine days in this stage. The first sign that a female dog is entering proestrus is a noticeable swelling of the vulva, followed by light to heavy bleeding. Dog owners can deal with the blood by purchasing doggy diapers at but they should note that diapers will not prevent their furry friends from becoming pregnant while they are in proestrus.

Swelling and bleeding are the most obvious physical signs that a dog is entering her heat cycle, but most pups also experience some behavioral changes. Personality changes vary by the dog, with some pets becoming more affectionate and others acting grumpy or standoffish. These personality changes aren’t always easy to spot, either. Changes in behavior toward other dogs are more obvious. Most dogs in proestrus will tuck their tail when other pups approach to guard their vulvas. Some dogs also experience changes in appetite.

Stage Two: Estrus
The estrus stage can last up to 21 days, but as with proestrus, most dogs experience the second stage of their heat cycles for an average of nine days. The estrus stage is when dogs become fertile and their ovaries release eggs for fertilization. It’s not until dogs reach the estrus stage that they become willing to mate. Instead of tucking her tail when other dogs approach, a female dog in estrus will move it to the side and welcome male dogs’ advances.

There are two physical changes that accompany the progression into the estrus stage. The first a lightened discharge. While a female dog’s discharge is bright red during proestrus, it will be closer to pink while she is fertile. The dog’s vulva will also soften as the initial swelling subsides.

Personality-wise, the biggest change from the proestrus stage to full estrus is that female dogs start behaving flirtatiously and welcoming the advances of males. They will make open advances by turning their rear ends towards male dogs and holding their tails out of the way. Many dogs also develop an elevated desire to run off and seek out suitable partners, so it’s extremely important for pet parents to keep an eye on their beloved animals while they are in estrus, whether they want puppies or not.

Stage Three: Diestrus
Diestrus, sometimes also referred to as metestrus, bring the fertile stage of the heat cycle to a close. The stage lasts between 60 and 90 days, but don’t worry. At this point, the dog is no longer fertile. If the dog has been impregnated, the diestrus stage will last until she gives birth to puppies. Her owners will need to take this time to prepare for the litter by taking the dog to the vet for check-ups, getting her prenatal vitamins or specialized dog food, and learning how to facilitate the birth safely at home.

Pet owners who didn’t want puppies, on the other hand, can breathe a sigh of relief when diestrus starts. Their dogs will no longer be interested in running off to find potential mates or making overt and awkward advances toward male dogs. Their personalities will return to normal and any lingering vulvar swelling will go down within a week. Provided dog owners’ have not allowed their beloved pets to leave their sight for long enough to get pregnant, they won’t have to worry about preventing puppies again until the estrus stage of the dog’s next cycle.

Stage Four: Anestrus
Anestrus is the resting stage. It lasts between 100 to 150 days, making it the longest stage of the full heat cycle. Dogs in anestrus are infertile until this stage ends, at which point the whole heat cycle starts over from the beginning. Most dogs only experience two heats per year.

How to Care for Dogs in Heat
The best way to prevent unwanted pregnancies is to have female dogs spayed, but not all dog owners want to put their pups through surgery. When dogs are in heat, make sure never to allow them outside unsupervised or let them go for walks off-leash. Placing a bit of menthol on the tip of the dog’s tail can help to mask her scent, making it easier to fend off unwanted advances from male dogs.

It’s important to be patient with dogs in heat. They may bleed on the floor, though it’s easy to prevent unwanted messes by training the dog to wear a doggy diaper. Many dogs will also need more attention from their owners, so be prepared to provide comfort, especially during the first two years of heat cycles.

The Bottom Line
All unspayed female dogs go through heat cycles from the time when they reach puberty onwards. Whether dog owners want to have puppies or not, they need to learn how to recognize the signs so they can help their pups manage their heat cycles more effectively. When in doubt about whether a behavior is normal, consult a vet.


  1. This was interesting to read

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