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How long does a girl dog stay in heat?

Female dogs go into heat cycles roughly twice per year once they reach sexual maturity. The heat cycle, also known as the estrus cycle, is part of the dog’s natural reproductive process. During this time, the female dog’s body is preparing for breeding and pregnancy. The heat period usually lasts 18-21 days from start to finish. However, this can vary between breeds and individual dogs. Understanding the stages of a dog’s heat cycle and recognizing the signs of heat are useful for dog owners who want to breed their dogs or prevent unwanted pregnancies.

What Is a Dog’s Heat Cycle?

A dog’s heat cycle occurs in four stages:


This first stage lasts approximately 7-10 days. During proestrus, estrogen levels increase, causing swelling of the vulva and bloody vaginal discharge. The discharge starts off red and then becomes lighter in color as the stage progresses. The female dog will lick and clean her genital area frequently. This is the early part of heat when the dog’s body is preparing for breeding. The female will be attractive to male dogs at this point but will usually not allow breeding.


The estrus phase lasts for around 5-10 days. The discharge becomes straw colored or pinkish in hue. The female dog will be very receptive to males and stand to be bred during this period. This is the optimal time frame for breeding to take place, as ovulation occurs towards the end of estrus. The dog’s behavior may change significantly, with increased nervousness, alertness and a desire to escape confinement or roam.


After standing heat, the discharge once again becomes redder in color. This stage lasts 50-90 days, sometimes longer in certain breeds. During diestrus the female dog’s reproductive tract is preparing for potential pregnancy. If no pregnancy occurs, the dog will go through a false pregnancy lasting up to 2 months. Female dogs typically do not go into heat during a false pregnancy.


This quiet phase occurs in between heat cycles. Vaginal discharge, swelling of vulva and attraction to males are not present. The anestrus period lasts approximately 3-4 months, although some dogs will go into heat again sooner. This brings the heat cycle back to the proestrus phase again for the next round.

What Are the Signs of Heat in Dogs?

Recognizing when your dog is going into heat is important, both for breeding purposes or to prevent an unwanted litter. Here are some key signs a dog is in heat:

– Swollen vulva
– Bloody discharge from the vulva, changing in color and amount based on the heat stage
– Increased urination
– Excessive licking of the genital region
– Change in temperament such as nervousness or aggression
– Strong odor from the genital area, which can attract male dogs
– Male dogs hanging around the home
– Crouching posture with tail moved to the side (this makes breeding easier)

Some female dogs also exhibit a small amount of bleeding from the vulva outside of their heat cycles. This can occur at times due to vaginal infections, urinary tract infections or anatomical abnormalities. Check with your veterinarian if you notice bleeding unrelated to heat.

How Long Are Dogs in Heat Each Cycle?

On average, the entire heat cycle from start to finish lasts about 21 days. However, this can vary between breeds and individual dogs. Some smaller breeds can cycle every 4-5 months, while larger breeds may only cycle once or twice per year. Here are some guidelines on heat cycle lengths:

– Proestrus: 7-10 days
– Estrus: 5-10 days
– Diestrus: 50-90+ days
– Anestrus: 3-4 months

So a typical 21 day heat period includes about 10 days of proestrus and estrus. The receptive period for breeding only lasts about 5-10 days. This is when ovulation occurs and the female should be bred if puppies are desired. If you notice bleeding for longer than 21 days, take your dog to the veterinarian to rule out medical issues.

At What Age Do Female Dogs Go Into Heat?

Most female dogs will have their first heat cycle between the ages of 6 and 12 months. However, some small breeds can go into heat as early as 4 months old. Large and giant breeds may not experience a first heat until 12-24 months old. Here are some general age guidelines for first heat by breed size:

– Small breeds – 4 to 12 months
– Medium breeds – 6 to 12 months
– Large/giant breeds – 9 to 24 months

Factors like nutrition, size of litter at birth, and hereditary traits can influence when heat first appears. If your female puppy has not gone into heat by age 2, it’s a good idea to consult your veterinarian. Late onset of puberty could point to an underlying health issue.

How Often Do Female Dogs Go Into Heat?

On average, unspayed female dogs will go into heat twice per year. This can vary anywhere from once every 4 months to once every 12-16 months. Here are some general guidelines on frequency of heat cycles:

– Small breeds – twice per year (about every 6 months)
– Medium breeds – twice per year (about every 6 months)
– Large breeds – once per year
– Giant breeds – once every 12-16 months

However, each dog is an individual and may not follow the average for their breed size. Older dogs and those with health issues may see irregular or absent cycles. Talk to your veterinarian if you notice your female dog is not cycling at the expected intervals.

How Long After Heat Can Dogs Get Pregnant?

Dogs are most fertile during estrus, which is when the egg is released for fertilization. This occurs about 2 days into the estrus phase, which lasts about 5-10 days within the full heat period.

Sperm can remain viable in the female dog’s reproductive tract for 5-7 days after breeding. So pregnancies can occur 5-7 days before ovulation, during ovulation, and 5-7 days after.

In total, female dogs can become pregnant over about a 12 day timeframe of the approximately 21 day heat cycle. This is why it’s so important to monitor your dog closely during her heat period if you do not intend to breed her. Accidental matings can easily result in surprise litters of puppies.

Can Dogs Get Pregnant When Not in Heat?

No, dogs cannot normally become pregnant if they are not in heat. The female’s body must undergo changes in hormone levels and physical changes to the reproductive organs during proestrus and estrus. This prepares optimal conditions for breeding and fertilization.

During anestrus and diestrus, pregnancies are extremely unlikely. The female dog is not releasing eggs to be fertilized, so conception usually does not occur.

There is a very small chance of conception at the very end of diestrus, as hormone levels start changing back into proestrus. However, fertility is reduced and litter size smaller if mating during diestrus results in pregnancy.

Can a Dog Stay in Heat Longer Than Normal?

It is possible but uncommon for dogs to have an abnormally long heat cycle, lasting more than 3-4 weeks from start to finish. Here are some reasons why heat may be prolonged:

– Low levels of progesterone – necessary for transitioning out of heat
– Persistent follicle on the ovary – keeps producing estrogen
– Anatomical problems such as cysts or infections
– False pregnancy
– Exposure to artificial lighting – can disrupt cycle
– Obesity
– Chronic illness

If you notice your dog having an unusually long heat cycle or one lasting longer than 4 weeks, take her to the vet. Treating any underlying medical conditions may help restore normal cycling.

When to Seek Veterinary Care

See your vet if your dog shows any of these signs related to heat:

– No heat by age 2
– Heat cycles less than every 4 months or longer than every 16 months
– Heat lasting longer than 4 weeks
– Abnormal discharge in between cycles
– Signs of false pregnancy such as milk production
– Appetite changes, lethargy or other concerning symptoms
– Difficulty or straining during urination
– Excessive licking of genital area

Your vet can run tests to check for conditions like urinary tract infection, reproductive disease, or hormone disorders. Treatment can help resolve abnormal heat cycles in female dogs.


The heat cycle lasts about 3 weeks on average for most female dogs. Small breeds tend to cycle more frequently than large breeds. The important period of heat when breeding occurs is estrus, which only lasts around 5-10 days. Most dogs go into heat every 6-12 months. Vets should be consulted if you notice your dog is not cycling normally or heats last longer than 4 weeks. Paying attention to signs of heat and your dog’s cycle timeline can help prevent accidental litters. While heat cycles can vary, familiarity with your dog’s normal routine makes it easier to notice when something may be off.

Breed Size First Heat Age Cycle Frequency Cycle Length
Small 4-12 months Twice per year 21 days
Medium 6-12 months Twice per year 21 days
Large 9-24 months Once per year 21 days
Giant 9-24 months Once every 12-16 months 21 days

Key Points

  • Proestrus lasts about 7-10 days
  • Estrus lasts about 5-10 days
  • Dogs are most fertile during the estrus phase
  • Entire heat cycle averages 21 days
  • Small dogs tend to cycle more frequently than large breeds
  • See your vet if your dog’s heat seems excessively short, long, irregular, or absent