How Long Are Dogs in Heat? Here’s the Answer
Key takeaways:
Most female dogs are in heat for 12 to 20 days, during which hormonal shifts prompt ovulation and behavioral changes that attract male dogs.
The heat cycle includes two stages, which are part of the four-stage canine estrous cycle.
Female dogs typically go into heat for the first time between the ages of 6 and 12 months, but that varies widely according to their breed and size.
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A common question among new dog owners raising female puppies is, “Do dogs have periods?” The short answer is, “No.” Dogs do not experience menstruation like people do. But they do experience the “canine estrous cycle,” which includes a period of bleeding known as a “heat cycle.”
For pet owners who have dogs who have not been spayed, it’s helpful to understand the full estrous cycle. Here’s everything you need to know to prepare for this stage of a female pup’s life.
How long does a dog’s heat cycle last?
A dog’s heat cycle consists of four stages. But when people talk about dogs in heat or a dog’s “period,” they’re typically referring to the first two stages. This part of a dog’s heat cycle lasts between 12 and 20 days.
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The final two stages of the full heat cycle vary in length, with diestrus lasting up to 3 months and anestrus averaging 4 months.
On average, unspayed female dogs typically experience two heats per year. Some breeds only cycle once per year, including Basenjis and Tibetan mastiffs.
Stages of canine estrous cycle
Only unspayed female dogs experience a heat cycle. The canine estrous cycle has four stages.
Spaying and neutering: There are many benefits to spaying or neutering your dog. Learn about some of them here, along with the best age to spay or neuter.
Lowering your vet bills: Read how one dog owner saved hundreds on her pup’s neuter surgery by shopping for a low-cost veterinary clinic.
Pet insurance coverage: Pet insurance can save you money, but it won’t cover everything. Here are common things pet insurance won’t cover for your dog.
Proestrus
During this stage, a dog’s ovaries produce the hormone estrogen. Proestrus typically lasts for about 9 days, but it can range from 3 to 17 days.
A dog experiencing proestrus typically produces a bloody vaginal discharge. At first, she may be aggressive or unreceptive to male dogs, who will likely be drawn to her.
Other signs of this cycle stage include:
Licking
Frequent urination
Increased vocalization
Swollen vulva
Estrus
During the estrus stage, a female dog’s estrogen levels fall and her progesterone levels start to increase. These hormonal changes, along with the continued production of follicle-stimulating hormone, prompt ovulation.
Estrus is also known as “standing heat.” A dog’s vaginal discharge will become lighter in color, and she may lift her tail or hold it off to the side to “flag” that she’s open to a male’s advances.
The estrus stage lasts between 7 and 10 days. The average female dog releases her eggs around the second day of this stage.
Diestrus
About 2 to 3 weeks after ovulation, during the diestrus stage, progesterone levels peak. After this, they slowly fall back to normal. Progesterone helps to maintain pregnancy. But these shifts in hormone levels will happen regardless of whether your dog is carrying puppies.
If your dog is not pregnant, you may not notice the hormonal changes. If she is pregnant, however, these are some telltale signs:
Enlargement of the mammary glands
Increased appetite
Milk production
Anestrus
Pregnant dogs give birth during anestrus, the final stage of the estrous cycle. It lasts an average of 4 months total, during which estrogen and progesterone levels are low. The uterus recovers and prepares for the next heat cycle during this stage.
When do female dogs go into heat?
Female dogs typically go into heat between ages 6 and 12 months old, but it can vary widely depending on the size of the breed. That’s because the first heat cycle typically occurs 2 to 3 months after a dog reaches its adult body size. So small breeds can start cycling early in life, sometimes even at 4 months old.
Keep in mind that some breeds won’t go into heat until they’re well into adulthood. For example, sighthounds — including greyhounds, borzoi, and Afghan hounds — typically don’t experience their first estrous cycle until they’re over 2 years old.
Do spayed dogs go into heat?
Spayed dogs do not go into heat. Spaying removes a dog’s ovaries, which prevents future production of estrogen and progesterone. Without these hormones, your dog cannot enter a heat cycle.
There are other health benefits of spaying your dog. These include:
Preventing uterine infections
Eliminating annoying mating-related behaviors, such as roaming around in search of a mate
Reducing the risk of mammary, ovarian, and uterine cancers
The bottom line
Dogs go into heat at the beginning of the estrous cycle. During this time, they may produce a bloody vaginal discharge for 12 to 20 days. They may also show other signs of being in heat, including licking, frequent urination, and loss of appetite. Dogs typically go into heat between 6 and 12 months of age, but this can vary depending on their size and breed. Spaying your female dog will prevent her from going into heat, as well as prevent certain health conditions.
Why trust our experts?
References
American Veterinary Medical Association. (n.d.). Spaying and neutering.
Bukowski, J. A., et al. (2011). Breeding and reproduction of dogs. Merck Veterinary Manual.
Cornell Richard P. Riney Canine Health Center. (2023). Dog estrous cycles.
Hess, M. (2023). The canine estrous cycle: Being in heat. Veterinary Partner.
Johnson, T. (2023). What to expect when your dog is in season. Veterinary Partner.
Lundgren, B. (2017). Keeping your pet healthy and happy. Veterinary Partner.
Threlfall, W. (2008). Canine estrous cycle and ovulation (proceedings). DVM360.
