The dog heat cycle in plain language, with a free calculator
A female dog comes into season about twice a year, and each season follows the same four stages. Knowing them tells you when she can conceive and when she cannot. This VerifiedStuds guide explains each stage, then helps you estimate her next heat.
Stage
Typical length
What you see
Proestrus
About 9 days (3 to 17)
Swollen vulva, bloody discharge, males interested but refused
Estrus
About 9 days (3 to 21)
Discharge lightens, she stands for a male, ovulation occurs
Diestrus
About 2 months
Heat ends, and she is pregnant or resting
Anestrus
About 4 months or more
No hormonal activity before the next cycle
Vets call the first two stages "heat" or "season". Together they last two to four weeks. So when people ask how long a dog is in heat, the honest answer is about three weeks, with wide variation.
Enter the first day of her last heat to estimate the next one. The result is a guide, because every female keeps her own rhythm.
During proestrus, the vulva swells and a bloody discharge appears. She may urinate more often and lick herself. Male dogs follow her, but she sits down or snaps when they try to mount.
Estrus is the fertile stage. The discharge usually turns pink or straw-colored, and the vulva softens. Most importantly, she stands still for a male and holds her tail to one side, which breeders call flagging.
In diestrus, the swelling goes down and she loses interest in males. Her body then behaves as if she is pregnant for about two months, whether she was bred or not. For that reason, some females show a false pregnancy.
Most dogs cycle about every six to seven months. However, the range is wide. Small breeds may cycle three times a year, while giant breeds may cycle once every 12 to 18 months. Basenjis and Tibetan Mastiffs usually cycle once a year.
First heat arrives between 6 and 24 months of age. Small dogs tend to start early, and large dogs late. In addition, young females are often irregular for the first couple of years, so do not worry if early cycles vary.
The old rule says to breed on days 9 to 14. It works for many dogs, but not for all. Ovulation can fall as early as day 5 or later than day 20. Therefore, a female bred "on the right days" can still miss.
The eggs also need about two days to mature after ovulation. As a result, the best breeding days come two to four days after she ovulates. Only blood tests can find that day reliably. Read our guides to progesterone testing for dogs and when to breed a dog in heat.
Keep her away from intact males. Dogs can mate through fences, and a tie takes only moments to begin.
Walk her on a lead. Her scent carries a long way, and she may try to roam.
Use washable pants indoors if the discharge is heavy, and change them often.
Write down the dates. The first day of bleeding is day one, and good records make the next cycle easier to plan.
Planning a litter this season? Then find a health-tested stud early, and check typical prices in the stud fee guide. Once she is bred, the dog pregnancy calculator gives her due date. Stud owners can list their stud free.
How long is a dog in heat?
About two to four weeks. Proestrus and estrus each last around nine days on average, but both vary widely.
How often do dogs go into heat?
Most cycle about every six to seven months. Small breeds can cycle more often, and giant breeds less often.
When is a dog most fertile in her heat cycle?
Usually two to four days after ovulation, which often falls between days 9 and 14. However, only progesterone testing can confirm it.
At what age does a dog have her first heat?
Between 6 and 24 months. Small breeds usually start earlier than large breeds.
Can a dog get pregnant on her first heat?
Yes, she can. However, vets and breed clubs advise waiting until she is physically mature and health tested.
Sources: VCA Animal Hospitals, estrous cycles in dogs, Merck Veterinary Manual, breeding management of bitches, American Kennel Club, dogs in heat. This page is general information, not veterinary advice.
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