Female dogs will have their first reproductive cycle once they reach puberty. Each cycle consists of several stages; the stage called estrus refers to when the female can become pregnant. Often, a pup that is in the estrus stage is said to be “in heat” or “in season.” But how long does a dog stay in heat is best answered with science.

Signs of a dog in heat

There are a few telltale signs of a dog in heat:

  • Her vulva will become enlarged, although this isn’t always very noticeable.
  • A bloody vaginal discharge can be seen at the beginning of your dog’s heat cycle. Over several days, that discharge will become watery and pink.
  • You may notice your dog urinating more often than usual, and she will show signs of marking. This is done to attract mates and let them know that she is in heat.
  • She may also seem to have dog anxiety, and will present herself to male dogs by raising her rump or holding her tail to the side.

How Long Does a Dog Stay In Heat?

Most female dogs stay in heat for about 2 to 4 weeks, although the exact length can vary depending on their age, breed, size, and overall health. Some dogs may only be in heat for around 10 days, while others can remain in their heat cycle for nearly a month.

During this time, your dog's hormone levels change as her body prepares for possible pregnancy. She is typically most fertile during the estrus stage, which often occurs after the initial bloody discharge becomes lighter or pink in color. However, because ovulation timing varies between dogs, it's possible for pregnancy to occur at different points throughout the heat cycle.

Even after the visible signs of heat begin to fade, your dog may still be fertile for a short period. If you do not plan to breed your dog, it's best to keep her away from intact male dogs for the entire duration of her heat cycle and for several days after the bleeding has stopped.

What Age Do Dogs Go Into Heat?

Dogs begin their heat cycles once they hit puberty, which can range between 6 months and 2 years of age depending on the size of the breed. Small dogs will reach puberty earlier than larger dogs. How often a dog goes into heat also varies based on their size. Canines will have 1-3 cycles per year, with the majority of dogs cycling twice a year (smaller dogs go into heat more often than larger dogs). On average, a dog will be estrus for 2-4 weeks. She is most fertile when her vaginal discharge becomes pink and watery, although it is possible for her to conceive at any time during her heat cycle.

How Often Do Dogs Go Into Heat?

Most female dogs go into heat about twice a year, or roughly every six months. However, how often dogs go into heat can vary depending on their breed, size, age, and individual reproductive cycle. While two heat cycles per year are common, some dogs may only go into heat once a year, while others, particularly smaller breeds, may experience three cycles annually.

In general, small breeds tend to have heat cycles more frequently because they mature faster, while large and giant breeds often have longer intervals between cycles. Younger dogs may also have somewhat irregular heat cycles as their bodies mature, but these typically become more consistent with age.

Keeping track of your dog's heat cycle can help you anticipate when her next cycle is likely to begin. Recording the start and end dates of each heat can also be useful information to share with your veterinarian, especially if your dog's cycles become unusually frequent, infrequent, or irregular. If you notice significant changes in your dog's normal cycle, it's best to schedule a veterinary exam to rule out any underlying health concerns.

What are the four stages of the canine heat cycle?

The four phases of your dog’s heat cycle are proestrus, estrus, diestrus, and anestrus.

Proestrus

Proestrus is the first part of the heat period where your dog’s body prepares itself for mating. This phase usually lasts around 9 days. Her vulva will swell and you may notice a blood-tinged discharge. Your dog may also hold her tail close to her body and act more clingy towards you than usual. At this stage of the heat cycle, your dog will start to attract males, but she will not be receptive to them and may growl or bite if they try to mount her.

Estrus

Estrus is the mating phase and usually lasts around nine days. During this time, her discharge will become less bloody. Female dogs will attract and accept males, and they will ovulate two to three days after mating. Your fur baby will likely mark spots in your home or outdoors with her urine. This sends the message that she is ready to breed. If an unneutered male dog is near, your female dog will likely present herself to him for mating.

Diestrus

This phase occurs directly after the “in heat” stage and lasts for about two months. Your dog’s body will either become pregnant or return to rest. Her vulva will return to normal size and the vaginal discharge will disappear.

Anestrus

Anestrus is the uterine repair phase. During this time, there is no sexual or hormonal behavior. This phase can last between 90 to 150 days before the next proestrus stage begins.

How Do You Know When a Dog's Heat Cycle Is Over?

As your dog's heat cycle comes to an end, you'll begin to notice several physical and behavioral changes. The swelling of the vulva gradually decreases, vaginal discharge stops, and your dog will typically return to her normal energy level and routine. Male dogs will also become much less interested in her as her fertility declines.

Although the visible signs of heat may disappear, it's important to remember that your dog may still be capable of becoming pregnant for a short time after the bleeding has stopped. To avoid an unplanned pregnancy, continue keeping her away from intact male dogs until your veterinarian confirms it is safe or until at least a few days after all signs of heat have ended.

Every dog's heat cycle is slightly different, so the timing of these changes can vary. Monitoring your dog's behavior and keeping track of her cycle can help you better recognize when her heat has ended and prepare for future cycles. If your dog's heat lasts significantly longer than four weeks or you notice persistent bleeding, unusual discharge, or signs of illness, contact your veterinarian for guidance.

How to prevent your dog from going into heat

Most pet owners (with the exception of dog breeders) decide to spay their female dogs before their first heat. Some experts believe this reduces the risk of mammary cancer and other conditions. It also eliminates the possibility of unwanted litters of puppies that have to be taken to shelters or euthanized. Spaying your dog is the only way to guarantee that she won’t become pregnant.

When Should You Spay Your Dog?

The best time to spay your dog depends on her breed, size, age, and overall health. While many veterinarians recommend spaying before a dog's first heat cycle to help reduce the risk of unwanted pregnancies and certain reproductive diseases, the ideal timing can vary. For some larger breeds, your veterinarian may recommend waiting until your dog is more physically mature before scheduling the procedure.

Spaying eliminates future heat cycles and prevents your dog from becoming pregnant. It can also lower the risk of conditions such as uterine infections (pyometra) and mammary tumors, particularly when performed before multiple heat cycles. Because every dog has unique health needs, it's important to discuss the timing of spay surgery with your veterinarian to determine the best approach for your pet.

Can Dogs Be Spayed While They Are in Heat?

Yes, dogs can be spayed while they are in heat, but the procedure is generally more complicated than a routine spay. During a heat cycle, the reproductive organs receive increased blood flow, making the surgery more technically challenging and increasing the risk of bleeding. Because of this, many veterinarians recommend waiting until the heat cycle has ended whenever possible.

If waiting isn't an option, such as to prevent an unintended pregnancy or for other medical reasons, your veterinarian may still recommend performing the surgery. The decision will depend on your dog's age, overall health, stage of the heat cycle, and your veterinarian's experience and recommendations.

If you're unsure whether your dog should be spayed while she is in heat, schedule a consultation with your veterinarian. They can evaluate your dog's individual situation and help you determine the safest time for surgery while discussing the benefits and potential risks of each option.

Tips for dealing with a dog in heat

If this is your first rodeo with a non-spayed dog, you may not know what to do when your dog is in heat. These simple tips will help make the process easier for you and your sweet pup.

  • Proper dog nutrition is important at all times, but especially for dogs in heat.
  • Pay special attention to her dog body language to help determine her needs.
  • Male dogs will be attracted to a female dog entering her heat cycle before she is receptive. Watch for defensive aggression that warns males to back off.
  • Even after your dog stops bleeding, she can still get pregnant. She’s much more likely to let a male mate after the bloody discharge stops.

When Should You Contact Your Veterinarian?

While most heat cycles are a normal part of a female dog's reproductive life, there are times when veterinary care is necessary. Contact your veterinarian if your dog experiences excessive bleeding, foul-smelling discharge, severe lethargy, loss of appetite, vomiting, fever, or signs of pain, as these could indicate an infection or another underlying health problem.

You should also reach out to your veterinarian if your dog's heat cycle lasts longer than expected, occurs unusually often, or if she has not gone into her first heat by around 2 years of age. Irregular heat cycles can sometimes be linked to hormonal imbalances or other medical conditions that require evaluation.

If your dog has accidentally mated with an intact male and you did not intend to breed her, contact your veterinarian as soon as possible to discuss your options. Your veterinarian can also answer questions about your dog's reproductive health, heat cycle, and the best timing for spaying based on her age, breed, and overall health.