About twice a year, the cycle takes over, and many dog owners feel surprisingly on their own with it. Here is the complete overview: what is normal, what your dog needs right now, and which weeks afterward deserve your attention.
A few dark drops on the kitchen tile, and suddenly you have a hundred questions. Is this normal? How long does it last? Can she still go to the dog park? And why has the neighbor's Labrador been acting like a lovesick teenager since yesterday?
elcome to the heat cycle, the chapter of owning a female dog that nobody really prepares you for. It is not an illness or an emergency, though. It is a completely normal part of life with an unspayed female dog. What it does demand is knowledge: about the phases, about the fertile days, which do not sit where most people assume, and about a window of time after the heat cycle that surprisingly few owners know about. Let's go through it step by step.
Unlike in humans, a female dog's bleeding is not menstruation. It is the opposite: it announces the fertile period instead of ending it. The whole process is directed by a finely timed interplay of estrogen, luteinizing hormone, and progesterone. You don't need to memorize the hormone curves. What matters is knowing that this interplay runs at its own pace in every dog. That is exactly why every number in this article is an average with an honest range, and why it pays off to know your own dog's cycle. More on that later.
The first heat arrives once a female dog is nearly full grown physically, and that depends heavily on her size:
| Size | First heat, typically |
|---|---|
| Small (under 10 kg) | around 4 to 8 months |
| Medium (10 to 25 kg) | around 6 to 12 months |
| Large (25 to 40 kg) | around 10 to 18 months |
| Very large (over 40 kg) | around 12 to 24 months |
A Chihuahua can be ready as early as four months, while a Great Dane female happily takes her time until two years, and both are normal. In certain breeds, like the Basenji or some sighthounds, only one cycle per year is even typical. Only if a female dog still hasn't had a heat by 24 months does that call for a veterinary checkup.
The first heat, by the way, is often a dress rehearsal with a few stumbles: weaker, shorter, and more irregular than the ones that follow, sometimes even a so-called split heat, which starts, stops, and then properly kicks off a few weeks later. That, too, is no cause for concern the first time around.
The complete cycle consists of four phases. You can see two of them, and two happen out of sight.
| Phase | Duration (average and range) | What you see |
|---|---|---|
| Proestrus | avg. 9 days, 3 to 21 days | Vulva swells, bloody discharge, males take interest, she rebuffs them |
| Estrus (standing heat) | avg. 9 days, 2 to 24 days | Discharge lightens, she tolerates males, turns her tail to the side |
| Diestrus | about 2 months | Nothing visible outside, hormonally in pregnancy mode |
| Anestrus | avg. 7 months, 5 to 14 months | Resting phase, nothing to see |
Proestrus is what most people perceive as the start of the heat cycle. The vulva swells, bleeding begins, and at the dog park a fan club forms surprisingly fast. The female herself usually wants nothing to do with it yet. She growls suitors away or simply sits down.
Estrus is the actual hot phase, the standing heat. The discharge lightens, often to a pale straw color, and her behavior flips. Now she stands still when a male tries to mount her and turns her tail to the side. This "standing" is what gives the phase its name, and it is the clearest sign that your dog can now be mated.
Diestrus and anestrus are phases you barely notice, even though a lot happens hormonally. During diestrus, the body runs a pregnancy program for about two months, whether or not she is actually pregnant. Two topics grow out of this program that get their own sections further down: false pregnancy and pyometra. After that comes anestrus, the long resting phase, until everything starts over.
The visible heat, meaning proestrus plus estrus, lasts about three weeks on average, with a normal range of two to four weeks. After that, the visible part is over, even though the body keeps working hormonally through weeks of diestrus.
For the interval between heat cycles, the rule of thumb is "about every six months," but it deserves the same breakdown by size as the first heat, something few guides carry through consistently. Small breeds tend to cycle more often, sometimes three to four times a year. Very large breeds take more time, occasionally with just one cycle a year. And within these ranges, every female dog has her own personal rhythm, which settles in after the first one or two heats and then stays remarkably consistent.
That consistency is your friend. It is not the calendar average across all dogs that tells you whether everything is normal for your dog, but her own established rhythm. A female dog who has always cycled every nine months and suddenly bleeds again after four months deserves a vet visit, even though four months would be perfectly normal for other dogs.
Along with swelling and discharge, behavior often changes, sometimes days before the first drop. Many female dogs become clingier or more irritable, mark outside noticeably more often, lick themselves more, or seem restless or off their food. Some suddenly cuddle like puppies, others want to be left alone. If you notice changes like these without an obvious reason, it is worth checking the calendar. For more on how to read behavior changes in general, see our article Why Is My Dog Suddenly Acting Different.
There are, however, two variants that can trick even attentive owners. Silent heat happens with normal ovulation but without noticeable outward signs: barely any swelling, barely any discharge, especially in very fastidious dogs who lick everything away immediately. She is still fertile, and a sudden crowd of interested males is often the only warning sign. You already know split heat from the chapter on the first heat: it starts, stops, and then comes back properly a few weeks later, this time with ovulation.
The takeaway from both is uncomfortable but important: don't rely on visible blood alone. Interest from males, behavior changes, and the calendar always belong in the picture too.
Here is where we clear up the most dangerous misconception. Many people assume that bleeding means fertile, and no more bleeding means safe. Biology works differently, and it works against you in two ways at once.
First, the fertile phase is not at the start but toward the back end. Ovulation happens only in estrus, once the discharge is already lightening, and the eggs still need two to three days after that before they are even capable of being fertilized. Second, dog sperm are marathon runners: they survive inside the female for at least seven days. A mating at the "harmless" edge of the heat cycle can therefore fertilize an egg that isn't ready until days later.
Taken together, this means the risky window is far wider than it feels, and it cannot be reliably narrowed down from the outside. For everyday life, there is really only one honest rule, and it is strict: from the first day of heat until several days after standing heat ends, keep her on leash and away from unneutered males, with no exception for the nice neighbor dog and no experimenting in the fenced meadow.
Now for the chapter that is missing from almost every guide and worth its weight in gold at the vet's office. Almost everyone recommends, somewhere in a side note, writing down when the heat cycle starts. Almost nobody explains why that is more than just being tidy.
The reason: for the veterinary workup of almost any cycle related issue, your dog's history is half the diagnosis. The clinic will ask when the last heat was, how long it lasted, and how far apart the previous ones came. With that information, they can judge whether a bleed could be a normal heat or is suspiciously early, whether a lethargic dog happens to be right in the critical pyometra window, and, for breeding dogs, when progesterone testing for timing a mating should start. Without a record, all of that starts with a shrug and a guess.
What you should record takes only a minute: the first day of bleeding, the day she starts tolerating males, the last day with any signs, plus notes like how heavy the bleeding was, her behavior, or a false pregnancy afterward. The Souldog app has its own heat cycle tracker for this, logging the start, duration, and anything unusual, and giving you a heads up before the next expected date. A notebook works just as well. What matters is that the data is there when the vet asks.
That leaves the practical part, and it is more relaxed than many people fear.
On hygiene: Most female dogs keep themselves surprisingly clean. Around the house, blankets on her favorite spots help, and a heat diaper if needed. Two honest notes on that: a heat diaper protects your furniture, it is not birth control, a determined male will not be stopped by one. And it should not stay on the dog around the clock, since damp fabric creates a climate where skin and mucous membranes get sore. Take it off regularly and let her clean herself.
On males: Your dog in heat gives off a scent that carries for miles and turns reliable males into hormone driven romantics. Expect strange dogs to show up where none ever have before, and even a well trained male's recall to fail once he is nearby. Fair consideration is part of the deal too: avoid busy dog parks and meet up spots during these weeks, and don't carry that scent through half the neighborhood unnecessarily.
On training class: Ask ahead of time, honestly. Many training schools request that dogs in heat sit out a session or two, since otherwise half the group stops paying attention to anything else. Scent work and training at home are the perfect alternative for these weeks.
Four to nine weeks after the heat cycle, some owners witness a strange spectacle: their dog builds nests, mothers stuffed toys, her mammary glands swell, and sometimes milk even comes in. That is false pregnancy, and it is not a behavioral problem, it is hormone biology. After diestrus, progesterone drops, prolactin rises, and the body runs the "puppies are here" program whether any puppies exist or not. In a mild form, this tendency exists in practically every unspayed female dog. It only becomes noticeable in some.
Mild cases go away on their own within one to three weeks. You can help by not encouraging nest building or mothering stuffed toys and by leaving the mammary glands alone, since any stimulation keeps milk production going. It is time to see the vet if she is visibly suffering, eating like a different dog, if the mammary glands become hot or painful, or if the whole show lasts longer than three weeks. The clinic can then help with prolactin inhibitors. And if the spectacle repeats after every heat cycle, that is a solid argument in the conversation about spaying.
Now for the most important safety topic in this article, and it starts with a number that should make you sit up: in large Swedish studies, on average about one in four unspayed female dogs develops pyometra, a pus filled uterine infection, by the age of ten. This is not a rare complication. It is a fixed part of the risk profile for unspayed female dogs, and the risk climbs with every year of age from about six onward.
The mechanism is directly tied to the cycle: during diestrus, progesterone remodels the uterine lining into a cozy breeding ground, and that exact environment is what bacteria can colonize. That is why pyometra has a typical time window that almost no guide names: it usually shows up four to six weeks after the heat cycle, with an observed range of two to sixteen weeks. Anyone who wrote down the heat cycle date knows exactly when heightened vigilance is called for.
These signs need immediate veterinary attention. Pus filled or blood tinged discharge from the vulva. Noticeably increased drinking and urinating. Fever, lethargy, loss of appetite, or vomiting in the weeks after a heat cycle. A belly that is increasingly swollen. Important: in the closed form, discharge is absent entirely, and the dog becomes severely ill quickly with no visible cause. Pyometra is an emergency. Left untreated, it ends in sepsis.
The good news: caught early, pyometra is very treatable, usually through surgery to remove the uterus and ovaries. The bad news doesn't need softening: caught late, it is life threatening. Between those two outcomes often stands only the question of whether someone knew the signs and knew the heat cycle date.
It happens even in the best families: an unwatched moment, a determined male, and suddenly the two are locked together. The first and most important piece of advice sounds paradoxical: do not pull them apart. The "tie" is anatomically normal, it releases on its own after a few minutes, and forcing them apart can seriously injure the female without even preventing a possible fertilization.
After that, stay calm and call the vet, but leave the panic behind. First, not every accidental mating leads to pregnancy by a long shot. A good share of the females involved simply don't conceive. Second, a pregnancy can only be confirmed reliably after about three weeks, by ultrasound or blood test. And third, for confirmed cases there are veterinary options for ending an unwanted pregnancy with medication. Which one applies depends on timing and belongs entirely in the vet's hands. Reputable clinics advise against any casual "morning-after shot" given without confirmation. What you can contribute, you already know by now: the date of the mating, when the heat cycle started, and the cycle history.
A common misconception to close out the biology part: female dogs do not go through menopause. The cycle keeps running for life, in principle. In old age it just becomes more irregular, the intervals longer, the signs weaker, and silent heats more frequent.
Two things follow from this. First, a twelve year old dog can still get pregnant, even if her last heat feels like a long time ago. Second, and more important, right when heats become less noticeable with age, the risks for pyometra and mammary tumors keep rising. That is why a simple rule applies to seniors: any bleeding that isn't clearly a normal heat, and any discharge out of the ordinary, should be checked out rather than written off to old age. For a broader look at keeping track of your older dog's quality of life, see our gentle checklist for senior dogs.
By the time the second heat with a false pregnancy rolls around at the latest, many owners start wondering whether spaying would be the better path. It reliably ends heat cycles and false pregnancies and essentially rules out pyometra. Against that stand real downsides, like the risk of incontinence and open questions about the right timing. There is no one-size-fits-all answer, and anyone who promises you one is making it too simple. That is why we dedicated a full, detailed article to this decision: Spaying and Neutering Dogs: What the Research Actually Says.
The first heat feels like a state of emergency. By the third, it is routine. Eventually you know that your dog always gets moody first and clingy after, that her rhythm sits at eight months, and that five weeks after it ends, you give her one extra watchful look.
That knowledge of her own pattern is the best protection you can give her, better than any rule of thumb from the internet. Keep track of the dates, whether in the Souldog app's heat cycle tracker or in a notebook, and the rest is calm observation. For more foundational knowledge on prevention and warning signs, check out our full overview of dog health.
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