How Do You Know When Your Dog Is In Heat?

You can tell if your dog is in heat by looking for physical and behavioral signs. These can include swelling of the vulva, blood or discharge from the vulva, more frequent urination, and behavior changes like increased attention-seeking.

Other signs may include restlessness, aggression or withdrawal, and changes in tail position. It’s important to note that these signs can vary between individual dogs and breeds. On average, a dog will go into heat about twice a year, but this can also vary.

Last Updated on September 20, 2023

Everybody knows I love dogs. But for some reason, female dogs have a special place in my heart. (Sorry male dogs!) They are affectionate, naturally submissive, and calm in nature. But one challenging part of being a pet owner of female dogs is their heat cycle. Whether you’re planning to breed her in the future or is still undecided about getting her spayed, you need to know the signs when she is in heat. It not only prevents unwanted pregnancy but keeps your dog away from dangerous situations (like running away from home).

Keep reading to learn about the dog heat cycle, their signs, and what to do while they’re going through it.Labrador Retriever

When can you expect your dog’s first heat?

According to the American Kennel Club, small breeds can start as young as 4 months old, while large breeds get their heat when they’re about 18-24 months old. But on average, most dogs will get their first heat between 6-15 months old. Additionally, experts recommend not breed your dog until they get past their first and second cycle. The eggs are not yet mature at this time, and the dog has not yet reached full maturity. Breeding too soon can negatively affect the dog and the puppies. If you plan to breed her, your vet can help determine when she can safely carry puppies

How can you tell if your dog is in heat?

Dogs, like all mammals, get their period. And the more knowledgeable you are of their cycle, the more you can prepare for it. Because trust me, things can get a little tricky when your dog is in heat. She will display changes in her behavior, like being more aggressive towards other females and being more ravenous than usual. Each of these signs will tell you which phase they are in their cycle.

Related: Can A Dog Get Pregnant When she’s Not In Heat? 

4 stages of the dog heat cycleGolden Retriever

Proestrus stage

The proestrus stage is the beginning of your dog’s heat cycle. This phase lasts for about 3-17 days, but on average most dogs will experience 9 days in this phase. The most telling sign would be the swelling of the vulva. You may notice her excessively licking her genital area to “clean” her bloody discharge. She may also be more anxious and on edge and will become clingier to you.

Furthermore, for some dogs, they may become more aggressive to male dogs at this time. She will tuck her tail between her legs or will sit down whenever another dog appears. If you notice any change in her appetite e.g. eating more or eating less, it may be a sign that she’s starting her period. Breast development is also a sign. 

Estrus stage

After a few days to a week, your dog is now ready to mate. You will notice that her discharge has become clear to straw-colored, and she will be initiating sexual interactions with male dogs. Her once swollen vulva is now softer. And you may see her move her tail from side to side, also known as “flagging” letting male dogs know she is fertile and ready to breed.

Be mindful though as male dogs can smell the pheromones she puts off from miles away and will want to get to her at any cost. It would be best to keep her out of the yard if you don’t want her to get pregnant. It may sound impossible, but no fence can keep male dogs from getting to her. Also, she may become more aggressive towards other female dogs at this time.

Diestrus stage

When the diestrus stage takes over, your dog is no longer interested in flirting. This phase can last for 60-90 days. You may notice that her vulva has stopped swelling, and her discharge is completely gone. By a week, if she isn’t pregnant, it will go back to normal. Some dogs, however, might act pregnant even though she isn’t. If you suspect her to be pregnant, take her to the veterinarian. He will be the one to confirm whether she is carrying puppies or a false positive. If she is pregnant, you can expect her puppies to arrive in 60 days.Dog sleeping on the floor

Anestrus stage

The anestrus stage is the final stage of the heat cycle. It’s also known as the resting stage and the longest phase in the cycle. Ranging from 100-150 days, this is the stage where she won’t show any hormonal or sexual behavior. When she reaches the end of this phase, a new heat cycle begins.

What do I do during this time?

There are many things you can do to make the experience less stressful for you and your dog. Here are some of them:

  • Walk her. Don’t let her heat stop you from taking a walk. She may benefit from it as it can help calm her down. Just make sure you keep her on a leash as male dogs won’t be able to resist her scent. Even if she is well-trained, her instinct to mate would be stronger.
  • As previously mentioned, don’t let your dog out in the yard. A male dog looking for a female in heat is relentless. If you’re not careful, you might find a strange dog tied to your female.
  • Ensure that your dog’s ID and microchip are up-to-date. In case she runs away, you can easily find her.
  • Keep your veterinarian’s contact number close. There are health issues like pyometra and uterine infection that your dog can experience after her heat cycle. More of this will be discussed in the next section.
  • Think about spaying your dog after her heat cycle is over. If you have no plans of breeding her in the future, it would be better if she gets spayed. There are various benefits to spaying your dog. 

How often do dogs go into heat?

Every dog is different. However, an unspayed dog usually goes into heat twice a year, roughly six months apart. Small breeds may cycle three times per year, while large breeds may only cycle once per year

Watch out for Pyometra

A few weeks after your dog’s heat cycle, she will be vulnerable to pyometra, a uterus infection. During her heat cycle, the white blood cells that protect your dog’s uterus from infection is not present. It enables sperm to enter but allows for infection to enter as well. If your dog exhibits a pus-like discharge from her vulva, contact your vet immediately. Other symptoms of pyometra are diarrhea, vomiting, restlessness, and fever. Dog in snow

Accidental mating?

Dogs can get an abortion. However, it’s important to note that abortion is not without risks. Abortion in dogs should only be for extreme emergency cases. If you want to read more about this, you can go ahead and jump right to Can Dogs Get Abortions? 


You won’t need much to know when your dog is in heat. If you observe her enough, you will notice a change in her personality and bleeding in her vulva. After a few days, the bleeding may get lighter, and she will want to be outside more to where other dogs are. If you don’t want her to get pregnant, you should keep her away from male dogs. If she does get mated, better start stocking up on puppy food! You can expect her puppies to be born in 60 days. If you suspect her to be pregnant, take her to the vet. 

All in all, if you want to avoid unwanted litters, it’s best to spay your dog. You can talk to your veterinarian about the best time and the benefits of spaying your dog. But until then, keep an eye out for signs of her heat cycle. You got this! 

Also related: What To Expect After Your Dog Is Spayed or Neutered

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