Dogs are mammals, just like us, but have you ever considered just what that means? A female dog goes through estrous cycles just like women do. While you may never have given much thought to dogs and their hormone cycles, to properly care for our female dogs, it’s essential to understand this process. Understanding how long are dogs in heat and what that cycle entails is critical to helping your dog become pregnant or preventing her from becoming pregnant. In the past, we’ve discussed what you can do for your dog while she’s in heat, but today we’ll tackle the ins and outs of the estrous cycle.

How Long Are Dogs In Heat?

The simple answer to “how long are dogs in heat” is about 2 to 4 weeks, but this can vary breed to breed and female to female.

The Canine Estrous Cycle

The canine estrous, or reproductive, cycle is made up of 4 stages: proestrus, estrus, diestrus, and anestrus. We can identify different stages based on physical appearance and behavior changes. Here is a general description of each part of the cycle.

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Proestrus is the stage in a female dog’s cycle when owners start noticing physical changes in their dog and her behavior changes. Male dogs are attracted to the female in this stage, but she is not receptive to them. During this phase, her estrogen levels peak and her follicles develop on her ovaries. Your dog’s vulva will appear swollen and have a blood-tinged discharge. This discharge is the reason many unspayed female dog owners use diapers during their heat cycle. Proestrus usually last for an average of 9 days, but it can range anywhere from 1 to 27 days in length.


Estrus is the stage of the cycle when the female is receptive to the male. Think of this as her “heat” phase. How long are dogs in heat? Like proestrus, this stage also lasts an average of 9 days, but it can range from 4 to 24 days long. Estrus is the portion of the cycle when a female is fertile. Her vulva is enlarged, but softer than in proestrus. There is more blood in her vaginal discharge. Estrogen levels are dropping while progesterone levels increase, helping the female’s body prepare for pregnancy. 

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Diestrus is the stage immediately following estrus, when the female is no longer receptive to a male. Think of this period as your female dog returning to “normal” after heat. This stage in how long are dogs in heat usually lasts about 2 months. During this time, estrogen levels are low but progesterone levels peak 3 to 4 weeks after the start of diestrus. 

By the end of this phase, progesterone levels decline to “basal” levels, or minimum levels. The decline in progesterone occurs whether the female has become pregnant or not. 


If your dog does not become pregnant, she will enter anestrus. Anestrus is the period of the heat cycle between diestrus and the next proestrus. Basically, anestrus is all the rest of the time your dog is not in heat. Unlike a female human, who experiences estrus every month, most dogs only experience 2 heat cycles per year. This means that female dogs spend 4 to 5 months at a time in anestrus. During this time, the vulva has returned to normal and is no longer swollen or experiencing discharge. Your dog’s body prepares itself for the next heat cycle and possible pregnancy.

How Do You Know If Your Dog Is Pregnant?

Now that we understand how long are dogs in heat and their heat cycle, let’s talk about what happens if your dog does become pregnant. Who in this world doesn’t love puppies? If you suspect your dog is expecting, congratulations! This new step is a big responsibility, however. Breeding a dog means caring for her during pregnancy and delivery, and your very first step should be a visit to the veterinarian to confirm the pregnancy. Learning the signs of labor and knowing when it’s likely to occur will help ensure your dog’s puppies are given their best chance from birth.

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Signs of Pregnancy in Dogs

While diagnostic tests are the only real way to determine if your dog is pregnant, there signs and symptoms to look for before rushing off to the vet. Signs of pregnancy in canines include:

  • An increase in appetite
  • Weight gain
  • Swollen belly
  • Increased affection
  • Increase in nipple size
  • Irritability
  • Tiring more easily
  • Nesting behavior
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Confirming Your Dog Is Pregnant

Commercial products don’t include canine pregnancy tests (yet!). If you suspect your dog is pregnant, the only accurate way to know for sure is to take her to the veterinarian. There are 4 ways a vet will check for pregnancy.

  1. Palpation: if you know what day the puppies were conceived, a veterinarian can gently palpate your dog’s abdomen between day 28 and day 30 of pregnancy. At this stage, the fetuses feel like small, round grapes, which are the fluid-filled sacs around each puppy. You should never attempt palpating on your own, as you could seriously injure the fetuses or your dog in the process.
  2. Hormone Test: Around 25 to 30 days into the pregnancy, your veterinarian can perform a blood test to confirm pregnancy. The blood test confirms the presence (or lack thereof) of the hormone relaxin, which is only produced during pregnancy. 
  3. Ultrasound: Between 25 and 35 days of gestation, your veterinarian can perform an ultrasound to look for fetal heartbeats.  Fetus’ heartbeats are 2 to 3 times faster than their mother’s, so they are easy to distinguish. In addition to confirming pregnancy, an ultrasound can give you an estimate of how many fetuses your dog is carrying.
  4. X-Ray: X-rays are probably the most effective way to confirm your dog is pregnant. This method is not effective, however, until around day 55 of gestation. Before then, the puppies skeletal systems are usually not substantial enough to see on the x-ray. X-rays give you an even better estimate of the number of puppies than an ultrasound.

Knowing Your Dog

A lot of answering questions like how long are dogs in heat is about knowing your dog. Having the scientific basis is essential for caring for our dogs, but each canine companion is an individual, and as such their cycles can be just as unique as they are. No one knows your dog like you do, so if you see problematic or worrying physical or behavioral changes in your pooch, consult with your veterinarian. The easiest way to prevent your female dog from having a heat cycle is simply to get her spayed.

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