Home / Breeding / Dog Heat Cycle
A female dog's reproductive cycle, called the estrous cycle, runs on hormones rather than on the calendar, and it looks quite different from a human cycle. There is no monthly rhythm and no menopause: an unspayed dog cycles, on average, about every six to seven months for her whole life. Understanding the four stages tells you when she can become pregnant, when to keep her under close guard, when breeding (if it is ever appropriate) would be timed, and when a pregnancy scare is actually impossible. If breeding is the goal, start with the responsibilities in our breeding hub before anything else.
| Stage | Typical length | What you see | Fertile? |
|---|---|---|---|
| Proestrus | About 6 to 11 days (can range 3 to 21) | Swollen vulva, bloody discharge, male dogs very interested, she refuses mating | No, but the fertile stage follows directly |
| Estrus | About 5 to 9 days (can range up to 20) | Vulva softens, discharge often lightens to a straw or pink color, she stands for males and flags her tail aside | Yes, ovulation happens in this stage |
| Diestrus | About 2 months | Discharge ends, vulva returns to normal, she refuses males again | No; the body runs the pregnancy hormone program either way |
| Anestrus | About 4 months (can run to 12) | Nothing at all; complete reproductive rest | No |
Proestrus is the stage most owners mean by "coming into heat". Rising estrogen swells the vulva and produces the characteristic bloody discharge, which can be heavy in a large dog or barely noticeable in a small, fastidious one who licks herself clean. Male dogs detect the change long before most owners do, and will gather, whine and attempt to reach her. She, however, is not receptive yet: she may sit down, snap, or turn on males who try to mount. Despite refusing mating, she is already a high escape risk, because the whole neighborhood knows her status. This is the stage for lead-only walks, no off-lead exercise, no unattended garden time, and a house-wide briefing that doors and gates matter for the next three weeks.
Estrus is standing heat, the stage in which she will accept a male. A surge of luteinizing hormone (LH) triggers ovulation partway through the stage, estrogen falls, progesterone begins its long rise, and her behavior flips from refusal to invitation: she stands still for males, moves her tail to one side, and may actively seek them out. Two pieces of reproductive biology make this stage treacherous for anyone relying on guesswork. First, ovulated eggs need 24 to 72 hours to mature before they can be fertilized. Second, sperm can survive for 5 to 11 days. So the fertile window is wider than the day of any single mating, and a mating early in estrus can produce puppies just as surely as one at its peak. Breeders who need accuracy use progesterone blood tests to find ovulation; owners who need safety simply treat the entire heat, plus a safety margin after it, as the risk period.
Whether or not she was mated, and whether or not she is pregnant, diestrus follows. Progesterone, the hormone that maintains pregnancy, peaks two to three weeks after ovulation and stays influential for roughly two months in every cycle. Her body, hormonally speaking, behaves as though pregnant, which is precisely why false pregnancy exists: when progesterone falls at the end of diestrus and prolactin rises, some dogs produce milk, nest and mother objects. Externally, diestrus is quiet: discharge stops, the vulva shrinks back to normal, and interest from males fades. If she was mated, this stage is when the pregnancy is confirmed and followed using the timeline in our week-by-week guide.
Anestrus is the long, silent interval between cycles, generally around four months and sometimes considerably longer. The uterus repairs itself after the exertions and hormonal exposure of diestrus, and nothing outward happens at all. The length of anestrus is what sets the overall spacing of heats: add the roughly three weeks of proestrus and estrus, two months of diestrus and about four months of anestrus and you arrive at the average six to seven month cycle. First heats arrive between about 6 and 18 months of age depending largely on size; cycles in young dogs can be irregular, including split heats that start, stall and restart, before settling into the individual's normal pattern.
Practical management matters more than products. Walk her on a lead, at quieter times, and be ready to turn away from approaching dogs; never leave her alone in a garden, because both she and visiting males can scale fences that look entirely adequate the other 49 weeks of the year. At home, washable covers and dog pants with disposable liners manage the discharge; expect some dogs to be clingy, restless, off their food or unusually sleepy, and give them a calm routine. Keep intact males in the same household completely separated for the full three weeks, behind two barriers rather than one, or board one of them elsewhere: determined dogs defeat single doors, crates and good intentions.
Spaying ends the cycle permanently, removes the risk of pregnancy and of the uterine infection pyometra, and, done before the early heats, reduces the risk of mammary tumors. The timing deserves a real conversation with your vet, because the ideal age varies with breed and size. Two scheduling points are well established: surgery is normally avoided while she is actively in heat, when tissues are more engorged, and it is best delayed until about eight to ten weeks after a heat has ended, because spaying during diestrus removes the progesterone source suddenly and can itself trigger a false pregnancy. Prices and what the operation involves are covered in our guide to spay and neuter costs (from the costs package).
If she was mated during a heat, intended or not, the next reads are signs of dog pregnancy and how long dogs are pregnant. Back to the breeding hub.
On average about twice a year, with a full cycle of roughly six to seven months between the start of one heat and the start of the next. The normal range is wide: some dogs cycle every four months, others once a year, and a few breeds, such as the Basenji, typically cycle just once annually.
Usually between 6 and 18 months of age. Small breeds often start towards the earlier end, large and giant breeds later, sometimes not until well past a year. She can become pregnant on that very first heat, even though she is far from physically mature.
The visible, outward part of heat, proestrus plus estrus, commonly runs about two to three weeks in total, though each stage individually ranges from a few days to about three weeks. The fertile days sit inside the second stage, estrus, and cannot be identified reliably by discharge color or behavior alone.
Pregnancy results from mating during estrus, the receptive stage when ovulation occurs. Because sperm survive for days and stage boundaries are fuzzy from the outside, the practical rule is stricter: treat her as at risk for the whole visible heat, and for several days after the signs fade.
Timing depends on breed, size, health and your plans, and it is a conversation for your vet. Two firm points: spaying removes heat cycles and pregnancy risk entirely, and surgery is normally scheduled away from an active heat and ideally eight to ten weeks after a heat ends, since spaying during the post-heat hormone phase can trigger a false pregnancy. Our spay and neuter cost guide covers prices.
A split heat starts with normal proestrus signs that stop before ovulation, then resume days or weeks later to complete the cycle; it is most common in young dogs. A silent heat is a normal cycle with ovulation but almost no outward signs, so the first evidence may be interested males, or a pregnancy. Both are reasons vets rely on hormone testing rather than observation when timing matters.
This page is general information drawn from the published guidance of the organizations listed under Sources below. It is not veterinary advice, and it does not replace your own veterinarian, who knows your dog. Pregnancy and birth carry real risks for the mother dog and her puppies. If you are worried about a pregnant, whelping or nursing dog, contact your veterinarian or an emergency clinic straight away. For a poisoning emergency, the ASPCA Animal Poison Control Center is on (888) 426-4435 and the Pet Poison Helpline on (855) 764-7661. A consultation fee may apply on the helplines.
Last updated: November 2026. Facts on this page were checked against the sources listed above. How we work: our methodology.