The Dog Heat Cycle Explained: 4 Stages, Timing and What to Expect
The dog heat cycle has four stages and lasts about six months from start to start. This vet-reviewed guide breaks down proestrus, estrus, diestrus, and anestrus, how long the bleeding lasts, and when to call your vet.
BVMS MRCVS
Medically reviewed by Dr. Pippa Elliott, BVMS MRCVS · Last reviewed
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The dog heat cycle is the reproductive rhythm that every unspayed female dog goes through, and understanding it takes the mystery out of the swelling, the bleeding, and the behavior changes you may be seeing. The full cycle, known medically as the estrous cycle, is divided into four stages and repeats roughly every six months. Only one of those stages, estrus, is the true fertile window when a female can become pregnant. This vet-reviewed guide walks through all four stages with their typical timing, when the first heat happens, how long the bleeding lasts, the signs to watch for, and the red flags that mean you should call your veterinarian right away.
- 1The dog heat cycle (estrous cycle) has four stages: proestrus, estrus, diestrus, and anestrus.
- 2The whole cycle repeats about every six months on average, though it ranges from roughly every 5 to 11 months depending on the individual dog and breed.
- 3The visible 'in heat' period, when a dog is bleeding and attracting males, lasts about two to three weeks; the truly fertile days fall within estrus.
- 4Bleeding is heaviest in proestrus and usually lightens or stops as the fertile phase (estrus) begins, so the amount of bleeding is a poor guide to fertility.
- 5Prolonged or excessive bleeding, foul or pus-like discharge, a swollen belly with lethargy after heat, or no heat by 24 months of age all warrant a veterinary call.
What Is the Dog Heat Cycle? (Estrous Cycle Basics)
In everyday language, people say a female dog is 'in heat,' 'in season,' or 'on heat.' The correct medical term for the whole recurring reproductive cycle is the estrous cycle. There is an important distinction hidden in the spelling: estrous (with the -ous ending) refers to the entire cycle of all four stages, while estrus (with the -us ending) refers specifically to the single fertile stage within it.
The cycle is driven by hormones, mainly estrogen and progesterone, that rise and fall in a predictable pattern. According to the Cornell Riney Canine Health Center and VCA Animal Hospitals, an intact female dog goes through this cycle roughly twice a year for most of her life. Unlike people, dogs do not go through menopause; a healthy unspayed female continues to cycle into her senior years, though the intervals may lengthen with age.
Knowing where your dog sits in her cycle matters for three practical reasons: it tells you when she can get pregnant, it explains the physical and behavioral changes you are seeing, and it helps you spot when something is wrong. The rest of this guide breaks the cycle into its four stages so you know what to expect at each point.
The 4 Stages of a Dog's Heat Cycle
The canine estrous cycle has four distinct stages, each with its own hormone pattern, physical signs, and typical duration. The durations below are averages; every dog is a little different, and the ranges are wide. Here is what happens in each stage.
Stage 1: Proestrus (about 6 to 11 days)
Proestrus is the start of heat and the stage most owners first notice. Estrogen levels rise, the vulva swells, and a bloody vaginal discharge appears. This is the classic 'my dog is bleeding' phase. Males become interested in her, but she is not yet receptive and will usually turn or sit down to reject them. Proestrus lasts about 9 days on average, with a normal range of roughly 6 to 11 days.
Stage 2: Estrus (about 5 to 9 days, the fertile window)
Estrus is the fertile stage, when the dog can conceive. Estrogen drops and progesterone begins to rise, ovulation occurs, and the female becomes receptive to males. A telltale sign is 'flagging,' where she moves her tail to one side and stands still to allow mating. The discharge often lightens from bloody to a straw or pinkish color during this stage. Estrus lasts about 9 days on average, commonly cited in the range of 5 to 9 days, though it can vary. VCA Animal Hospitals notes estrus averages about 9 days but can range widely, from as little as 2 days to as long as 24 days in some dogs.
Stage 3: Diestrus (about 2 months)
Diestrus follows estrus, whether or not the dog is pregnant. Progesterone dominates this stage. If the dog conceived, this is the period of pregnancy, which lasts about 63 days. If she did not conceive, her body still goes through a progesterone-driven phase of similar length, which is why some dogs experience a false pregnancy with nesting or milk production even without being pregnant. The vulva returns to normal size and the discharge stops. Diestrus lasts roughly two months.
Stage 4: Anestrus (about 4 months, reproductive rest)
Anestrus is the resting phase between cycles, when there is no reproductive activity and hormone levels are low. There are no outward signs of heat, and the uterus recovers and prepares for the next cycle. Anestrus lasts about four months on average, and its length is the main reason the interval between heats is roughly six months. When anestrus ends, proestrus begins again and the cycle repeats.
Here is how the four stages compare at a glance:
| Stage | Typical length | Main hormone | What you see |
|---|---|---|---|
| Proestrus | About 6 to 11 days | Estrogen rising | Swollen vulva, bloody discharge, males interested but female not receptive |
| Estrus (fertile) | About 5 to 9 days | Estrogen falling, progesterone rising | Discharge lightens, female receptive and flagging, ovulation, can conceive |
| Diestrus | About 2 months | Progesterone | Discharge stops, vulva shrinks, pregnancy or return to baseline, possible false pregnancy |
| Anestrus | About 4 months | Low (resting) | No signs of heat, reproductive rest before the next cycle |
When Does a Dog Have Her First Heat, and How Often?
Most female dogs have their first heat between 6 and 24 months of age. The timing depends heavily on size and breed. Small breeds tend to reach their first heat earlier, sometimes as young as 4 to 6 months, while large and giant breeds may not cycle until 18 to 24 months. On average, the first heat arrives around 6 months, but a delay in a large breed is usually normal.
After the first cycle, most dogs come into heat about twice a year, or roughly every six months. The interval varies: some dogs cycle every 5 to 7 months, others closer to every 8 to 11 months, and both can be normal for the individual. What matters is that your dog is fairly consistent for herself once she matures. Early cycles in a young dog can be irregular before settling into a pattern.
There are notable breed exceptions. Basenjis and Tibetan Mastiffs typically cycle only once a year, an ancestral trait tied to seasonal breeding. If you have one of these breeds, once-yearly heats are expected and not a cause for concern. If any dog goes past 24 months with no sign of heat, that is worth a veterinary check to rule out an underlying issue.
How Long Does a Dog Stay in Heat (and Bleed)?
The full estrous cycle spans about six months, but the part owners mean when they ask how long a dog is in heat is the visible window of proestrus plus estrus. Combined, that is usually about two to three weeks. During this window the vulva is swollen, discharge is present, and the dog attracts and eventually accepts males.
Bleeding is a separate question from fertility. The bloody discharge is heaviest in proestrus, the first phase, and typically lightens to a pink or straw color and then tapers off as estrus begins. So a dog often bleeds most when she cannot yet conceive, and bleeds least during her most fertile days. For a detailed breakdown of how long dogs bleed in heat, the short version is that visible bleeding usually lasts around 7 to 10 days, though some dogs bleed more lightly or 'clean themselves' so thoroughly that owners barely notice it.
Because the amount of bleeding is such an unreliable signal, do not use it to judge when your dog is fertile or when it is safe to relax supervision. The safest assumption is that she can conceive at any point during the roughly three-week heat, and unspayed males should be kept well away for the entire time.
Signs and Symptoms Your Dog Is in Heat
Heat brings a mix of physical and behavioral changes. Not every dog shows all of them, and some are subtle, but the following are the most common signs owners notice:
- Swollen vulva: often the first physical sign, appearing in proestrus and sometimes noticeable a few days before bleeding starts.
- Bloody to straw-colored discharge: heaviest and reddest early on, lightening as she moves toward her fertile days.
- Increased urination and marking: she may urinate more often and in small amounts to spread scent that signals her status to males.
- Flagging and receptivity: during estrus she may hold her tail to one side and stand still around males, a clear sign she is in her fertile window.
- Behavior changes: some dogs become clingy or restless, others irritable or withdrawn; increased licking of the genital area is also common.
- Attracting male dogs: intact males can detect a female in heat from a long distance and may appear at your property, so supervision matters.
For a fuller walk-through of what to look for and how the signs change stage by stage, see our guide to dog in heat symptoms. If any sign seems extreme, such as very heavy bleeding, obvious pain, or a foul-smelling discharge, treat it as abnormal and call your vet rather than assuming it is just part of heat.
How to Know When the Heat Cycle Is Over
Knowing when heat has ended matters for safety: it tells you when the risk of an accidental pregnancy has passed and when you can relax supervision. There is no single test at home, but several signs together tell you the visible heat is winding down:
- The discharge stops: bleeding and any straw-colored discharge fade and then cease as she leaves estrus.
- The vulva returns to normal: the swelling gradually subsides back to its usual size over a few days.
- Males lose interest: she stops attracting male dogs and is no longer receptive to them.
- Behavior settles: restlessness, clinginess, and marking ease back toward her normal baseline.
As a rule of thumb, the visible heat is usually finished about three weeks from the day bleeding first appeared. To be safe, most vets advise keeping her separated from intact males for a few extra days after the discharge fully stops, because the tail end of the fertile window can linger slightly. If you are ever unsure whether the fertile period has truly passed, your vet can check with a progesterone test.
Can a Dog Get Pregnant During Heat? (The Fertile Window)
Yes, and this is the single most important safety point of the whole cycle. A dog can become pregnant during estrus, the fertile stage. Ovulation happens a few days into estrus, and the most fertile days are generally the last 4 to 5 days of the estrus phase. However, because eggs need time to mature and sperm can survive in the reproductive tract for up to about a week, the practical fertile window is wider and less predictable than most owners expect.
A single unsupervised meeting with an intact male can result in a litter. If a mating happens and you did not intend it, contact your veterinarian promptly, because there are time-sensitive options to discuss. If you are planning a litter, our partners at Petful have a helpful guide to pregnant dog care that pairs well with veterinary guidance once pregnancy is confirmed.
If your dog does conceive, gestation runs about 63 days. Our full guide to how long dogs are pregnant walks through the timeline week by week. The only way to time the fertile window precisely, whether you are trying to breed or trying to avoid it, is progesterone testing with your veterinarian.
The 7-7-7 Rule for Dogs in Heat
The '7-7-7 rule' is a simple owner heuristic for remembering the rough shape of a heat. It divides the visible heat into three seven-day blocks: about 7 days coming into heat (early proestrus), about 7 days of the fertile, standing-heat window (estrus), and about 7 days going out of heat. Add those up and you get the familiar roughly three-week visible heat.
The 7-7-7 rule is a memory aid, not a biological fact. Real dogs vary widely: proestrus can run 6 to 11 days, estrus 5 to 9 days or more, and the fertile window does not fall on the same days for every dog. Treat 7-7-7 as a loose planning guide for supervision, and never as a precise fertility calendar. If accurate timing matters, only progesterone testing at the vet can pinpoint ovulation.
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How to Care for Your Dog During Her Heat Cycle
Heat is a normal event, not an illness, and most dogs sail through it with a little extra care. Your two priorities are keeping her clean and comfortable and preventing an unplanned pregnancy. Practical steps include:
- Manage the mess with hygiene wear: washable dog diapers or belly bands catch discharge and protect furniture and bedding. Change them regularly to keep her skin healthy.
- Supervise every outing: keep her on a leash for all walks and never leave her alone in an unfenced yard, where a determined male could reach her.
- Keep intact males away: avoid dog parks, daycare, and off-leash areas during the entire heat, and separate her from any unneutered males in your own home.
- Offer comfort and routine: keep her normal feeding and exercise routine, give her a quiet space to rest, and be patient with any moodiness or clinginess.
- Clean up promptly: an enzymatic pet cleaner handles any discharge on floors or bedding and helps remove scent that draws males.
Any home care and products are adjuncts to sensible supervision, not a substitute for it. Diapers and belly bands manage mess but do not prevent mating, so they never replace physically keeping intact males away. If your dog seems genuinely distressed, in pain, or unwell during heat, that is a reason to call your veterinarian rather than to push through it.
Spaying: How It Ends the Heat Cycle and When to Do It
Spaying (ovariohysterectomy, the surgical removal of the ovaries and usually the uterus) permanently ends the heat cycle. A spayed dog no longer comes into season, cannot become pregnant, and no longer attracts males. It is the definitive way to stop the cycle for good.
Beyond preventing unwanted litters, spaying carries real health benefits. According to the American Veterinary Medical Association and VCA, spaying eliminates the risk of pyometra (a life-threatening uterine infection common in older intact females) and greatly reduces the risk of mammary tumors, especially when done before or after only a few heat cycles. It also removes the risk of ovarian and uterine cancers.
The best age to spay is an individual decision. Traditionally many dogs were spayed around 6 months, before the first heat, but current guidance increasingly tailors timing to breed and size, since some large breeds may benefit from waiting until they finish growing. This is a conversation to have with your veterinarian, who can weigh your dog's breed, size, health, and lifestyle.
Spaying is not usually performed during an active heat, because the reproductive tract is engorged and the bleeding risk is higher, so vets often wait a couple of months after heat ends. If an accidental mating occurred, ask your vet promptly about mis-mate options, as these are time-sensitive.
When to Call Your Veterinarian
Most heat cycles are uneventful, but a few situations signal a problem that needs prompt veterinary attention. Learn these so you can tell a normal heat from a red flag.
Beyond emergencies, book a non-urgent vet visit if your dog has not had a first heat by 24 months of age, if her cycles are wildly irregular or unusually frequent (heats less than about four months apart), or if she shows signs of a false pregnancy that are distressing or persistent. Any suspected mating you did not plan is also worth a call, since your vet can discuss options and monitor her. When in doubt, phone your veterinary team; they would far rather answer a false alarm than miss something serious.
Spaying vs. managing heat cycles at home
Pros
- Spaying permanently ends heat cycles, unplanned pregnancy risk, and the mess and stress of managing a dog in season.
- It eliminates the risk of pyometra and greatly lowers the risk of mammary tumors, especially when done early.
- No more twice-yearly supervision windows, diapers, or keeping intact males at a distance.
Cons
- Spaying is major surgery with anesthesia and a recovery period, and timing should be tailored to breed and size with your vet.
- Managing heat at home keeps the option of breeding open but demands vigilant supervision every cycle to prevent an accidental litter.
- Home management does nothing to reduce the long-term risks of pyometra and mammary tumors that spaying addresses.
Frequently Asked Questions
Frequently Asked Questions
How long is a dog in heat bleed?
Most dogs bleed for about 7 to 10 days during heat. The bleeding is heaviest at the start, in the proestrus stage, then usually lightens to a pink or straw color and tapers off as the fertile estrus stage begins. Some dogs bleed more lightly than others, and very tidy dogs clean themselves so well that owners barely notice. Remember that the amount of bleeding is not a reliable guide to fertility, because a dog often bleeds most when she cannot yet conceive and least during her most fertile days.
What is the 7 7 7 rule for dogs?
The 7-7-7 rule is a simple memory aid for the rough length of a dog's heat. It splits the visible heat into three seven-day blocks: about 7 days coming into heat, about 7 days of the fertile standing-heat window, and about 7 days going out of heat, which adds up to the familiar roughly three-week season. It is only a rule of thumb, not a biological fact. Real dogs vary a lot: proestrus can last 6 to 11 days, estrus 5 to 9 days or more, and the fertile days do not fall on the same dates for every dog. Use it as a loose planning guide, never as a precise fertility calendar.
How do you know when a dog's heat cycle is over?
You can tell a dog's heat cycle is over when several signs come together: the bloody and straw-colored discharge stops, the swollen vulva returns to its normal size over a few days, male dogs lose interest and she is no longer receptive, and her behavior settles back to normal. As a rule of thumb, the visible heat is usually finished about three weeks after bleeding first appeared. To be safe, keep her away from intact males for a few extra days after the discharge fully stops, because the tail end of the fertile window can linger. If you are unsure whether the fertile period has truly passed, your vet can confirm with a progesterone test.
How often do female dogs go into heat per year?
Most female dogs go into heat about twice a year, or roughly every six months. There is normal variation: some dogs cycle every 5 to 7 months and others closer to every 8 to 11 months, and both can be normal for the individual dog once she matures. Small breeds often cycle a little more frequently, while some large and giant breeds cycle less often. A few breeds, notably Basenjis and Tibetan Mastiffs, typically come into heat only once a year. If your dog's cycles are extremely frequent (less than about four months apart) or she has not had a first heat by 24 months of age, check with your veterinarian.
How can I tell when my dog's heat is finished?
You can tell your dog's heat is finished when the discharge has completely stopped, the vulva has shrunk back to its usual size, she no longer attracts or accepts male dogs, and her behavior has returned to normal. This typically happens around three weeks from the first day of bleeding. Because these are the same signs that mark the end of the fertile window, the safest approach is to continue supervising her and keeping intact males away for a few days after everything appears to have returned to normal. If you need certainty, especially before allowing her around intact males again, your veterinarian can confirm with a progesterone test.
Do female dogs get periods like humans?
Not in the same way. Although a dog in heat bleeds, the canine estrous cycle is different from a human menstrual cycle. In people, bleeding happens when the uterine lining sheds after ovulation if there is no pregnancy. In dogs, the bloody discharge occurs in proestrus, before ovulation, and is caused by rising estrogen, and the female is fertile after the bleeding lightens rather than being infertile during it. So while owners sometimes call it a dog's 'period,' the biology and timing are not the same as a human period.
Do male dogs go into heat?
No. Only female dogs have a heat cycle. Male dogs do not go into heat or cycle; once they reach sexual maturity, they can breed at any time of year. What people sometimes describe as a male 'going into heat' is really a male reacting to a nearby female who is in heat. Intact males can detect a female in season from a considerable distance and may become restless, vocal, or determined to escape and reach her, which is exactly why supervising an in-heat female and keeping intact males away is so important.
Editor
The Webvet Editorial Team is the in-house group of pet-care editors and writers behind Webvet, operated by Smart Pet Collective. The team researches, writes, and maintains Webvet's pet health, behavior, and medication content. Every article follows a defined editorial process: research from reputable veterinary and scientific sources, careful drafting, mandatory review of medical content by a credentialed veterinarian, and dated publication. Health and medication articles are medically reviewed by a licensed veterinary professional before they go live and are kept current over time.
Veterinarian · BVMS MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty Puggle named Poggle, 3 cats and a bearded dragon.
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