Dog Heat Cycle Stages

What are the four stages of a dog's heat cycle?

A dog's heat cycle has four stages: proestrus, estrus, diestrus, and anestrus. Only the first two look like heat. Proestrus is the bleeding stage, lasting on average 6 to 11 days, when she attracts males but will not accept one. Estrus is the receptive stage, usually 5 to 9 days, when mating can happen and ovulation occurs. Diestrus follows for about two months, when progesterone stays high whether or not she is pregnant. Anestrus is the quiet resting stage, lasting about four to five months, before the next cycle begins.

Most dogs go through this whole sequence about twice a year. But the stages do not run on a fixed calendar. Cornell University College of Veterinary Medicine stresses that there can be extreme variation between individual dogs in both behaviour and physical signs in each stage, so the day counts below are averages with real ranges, not deadlines.

The four stages at a glance

Stage	What you see	Hormones	Typical length
Proestrus	Bloody discharge, swollen vulva, attracts males, not receptive	Estrogen rises and peaks	6 to 11 days on average (Cornell)
Estrus	Discharge lightens to straw or salmon colour; she stands for mating, flags her tail	Estrogen falls, progesterone rises, LH surge	Usually 5 to 9 days; range 1 to 20 days (Cornell)
Diestrus	No discharge, no interest in males, vulva back to normal	Progesterone high, then slowly falls	About 60 days
Anestrus	Nothing visible; resting stage	Progesterone low	About 4 to 5 months

Stage 1: Proestrus — the bleeding stage

Proestrus is the start of heat, and it is the stage most owners notice first. Estrogen produced by the ovaries rises and peaks one to two days before estrus begins. That estrogen causes the two classic signs: bloody vaginal discharge and swelling of the vulva.

During proestrus, a female dog will be attractive to male dogs and may play with them, but she is not yet receptive to breeding. She will usually turn a male away, sit down, or snap at him if he tries to mount. This stage lasts, on average, between six and eleven days (Cornell).

What to watch for:

• Swollen vulva, often the first physical sign, sometimes before any blood appears
• Bloody discharge, which may be heavy in some dogs and light in others
• More frequent urination, which spreads pheromones that signal males
• Male dogs showing interest, following her, or hanging around the house or garden
• Restlessness or clinginess, though many dogs behave normally

A practical point: day 1 of the cycle is the first day of swelling or discharge, not the first day a male dog notices her. If you ever need to time a breeding or a spay, that day 1 date is the anchor everything else is counted from.

Stage 2: Estrus — the receptive stage

Estrus begins when the female becomes receptive to breeding. The hormonal trigger is a surge in luteinising hormone (LH), caused by falling estrogen and rising progesterone. The LH surge is the central event of the whole cycle: ovulation follows it by about two days, and the fertile window opens about two days after that, once the eggs have matured.

Outwardly, estrus looks different from proestrus. The discharge often changes from bloody to a lighter, straw-coloured or salmon-coloured, watery flow, though Cornell and the VCA both note that many variations exist between individuals. She will stand still for a male, present her hindquarters, and flag her tail to the side. The VCA says most dogs become receptive around seven to ten days into the cycle, and ovulate around the eleventh day.

Estrus usually lasts five to nine days but may vary between one and twenty days (Cornell). That wide range is the reason counting days from the first spot of blood is a poor way to time a mating. The Merck Veterinary Manual gives the fertile days as days 4 to 7 after the LH surge, with days 5 and 6 the most fertile, because ovulation is on day 2 and the eggs need 2 to 3 days to mature.

What to watch for:

• Discharge lightening in colour and becoming thinner
• Standing still and flagging her tail when a male approaches
• Actively seeking out male dogs rather than avoiding them
• The vulva softening after the firm swelling of proestrus

If you are planning a mating, this is the stage where testing matters. Progesterone blood tests taken every two to three days can pinpoint the LH surge and ovulation, and the dog progesterone calculator turns those results into a breeding window.

Stage 3: Diestrus — the quiet two months

Diestrus begins when the female no longer shows signs of estrus, such as standing to be mounted. It is easy to miss, because from the outside she simply looks like a normal, non-heat dog again. Inside, a lot is happening.

Progesterone, the pregnancy maintenance hormone, rises during diestrus whether or not the dog is pregnant. It peaks 2 to 3 weeks after ovulation, stays high for another 1 to 2 weeks, then slowly decreases over 10 to 30 days (Cornell). Diestrus ends when progesterone returns to baseline. In total it lasts about 60 days, which is no coincidence: it is the same length as a pregnancy, because the body runs the same hormonal programme either way.

This is also why false pregnancy happens. As progesterone falls at the end of diestrus, the body can behave as though it has given birth: mammary enlargement, milk, nesting, and mothering behaviour in a dog that was never pregnant. The signs usually begin 4 to 9 weeks after heat and resolve in about 14 to 21 days (VCA). Only a relaxin blood test or an ultrasound can distinguish a false pregnancy from a real one, because progesterone rises in both.

During diestrus, females are no longer attractive to males and will not allow mating. If she was mated during estrus, this is the pregnancy itself: about 63 days from ovulation. You can work out the dates with the dog due date calculator.

Stage 4: Anestrus — the resting stage

Anestrus is the stage a dog enters at the end of her heat cycle, or after having a litter. Progesterone stays low throughout. The uterus undergoes involution, a repair process that prepares it for the next cycle, which takes about four months to complete (Cornell).

Nothing visible happens in anestrus. No discharge, no swelling, no interest from males, and usually no behavioural change at all. It is the longest stage, roughly four to five months, and it is the reason most dogs cycle only about twice a year. A dog in anestrus cannot get pregnant, and there is nothing to track until the next proestrus begins.

How the stages fit into one year

For a typical dog cycling twice a year, the year looks roughly like this:

• Heat (proestrus + estrus): about 2 to 3 weeks
• Diestrus: about 2 months
• Anestrus: about 4 to 5 months
• Then the sequence repeats

That adds up to a cycle every 5 to 11 months on average (Cornell), or an interval of 4 to 12 months with an average of about 7 months (VCA). Small breeds tend to cycle more regularly and more often; large and giant breeds less often. The Basenji and Tibetan Mastiff are exceptions that typically cycle only once a year.

What can go wrong with the stages

Most cycles run their course without problems, but a few patterns are worth knowing:

• Silent heat. The dog ovulates but shows few or no outward signs, so the heat is missed entirely. First heats are often silent (VCA). Only progesterone testing or vaginal cytology can confirm it happened.
• Split heat. Proestrus starts, then stops for days or weeks before starting again. It is common in young dogs whose cycles are still settling.
• Prolonged proestrus or estrus. Bleeding that goes well beyond three weeks, or a receptive stage lasting far past the usual range, should be checked by a vet.
• No heat by the expected age. A first heat usually comes between 6 and 24 months (Cornell). A dog with no heat by 2 years of age should be examined.
• Bleeding between cycles. Discharge outside proestrus and estrus is not part of a normal cycle and needs a vet visit, particularly if it smells bad or the dog seems unwell.

Related guides

• How long is a dog in heat
• How often do dogs go into heat
• Best time to breed a dog
• Dog Due Date Calculator

Frequently asked questions

How long is each stage of a dog's heat cycle?
Proestrus averages 6 to 11 days, estrus usually 5 to 9 days (range 1 to 20), diestrus about 60 days, and anestrus about 4 to 5 months (Cornell). The two visible visible stages together make the 2 to 3 weeks most people call heat.

Which stage can a dog get pregnant in?
Only estrus. That is the receptive stage, when ovulation happens. She cannot conceive in proestrus, diestrus, or anestrus.

What is the difference between proestrus and estrus?
In proestrus she bleeds, her vulva swells, and she attracts males but will not accept one. In estrus the discharge lightens, she stands for mating, and ovulation occurs. The change in discharge colour and her willingness to stand are the practical signs that one stage has ended and the other begun.

How do I know which stage my dog is in?
Watch the discharge and her behaviour: bloody discharge plus refusal means proestrus; lighter discharge plus standing and tail flagging means estrus; no discharge and no interest means diestrus or anestrus. For certainty, a vet can use vaginal cytology or progesterone blood tests.

Can a dog be in diestrus and not be pregnant?
Yes, and this is normal. Progesterone rises in diestrus whether or not she conceived. That is also why false pregnancy happens: the hormonal programme runs the same way either way.

Does a dog have all four stages every cycle?
Yes. Every cycle runs through all four stages in order. What varies is how obvious each stage is: proestrus and estrus are visible, diestrus and anestrus are not, and in a silent heat even the visible stages can be hard to spot.

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This article is educational only. Cycle lengths vary between dogs, and a calculator result is an estimate, not a diagnosis. If your dog's cycle seems unusual, or you are planning to breed, ask your veterinarian.

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Sources

• Cornell — Dog Estrous Cycles
• VCA — Estrus and Mating in Dogs
• VCA — False Pregnancy in Dogs
• Merck — Serologic Test Kits