Dog Heat Cycle: Stages, Signs and How to Care for Her

The four stages of the heat cycle

VCA Animal Hospitals and the AKC both describe the cycle in four stages. Proestrus comes first, averaging about nine days with a range of roughly 3 to 21. Vulvar swelling and bloody discharge appear, and males take notice, but she is not yet willing to mate. Estrus follows, also about nine days on average, and this is when she accepts a male. The discharge usually turns watery and pinkish.

Diestrus comes next and averages around 60 days. She is no longer fertile, and the swelling and discharge should stop. Then anestrus, a quiet resting phase of about four to six months, resets the cycle. When people say a dog is in heat, they usually mean proestrus and estrus together. Dogs typically cycle about every six months, or twice a year, though that varies by breed.

When the first heat happens

The timing depends on size. VCA gives an average of about six months, with small breeds starting earlier and large or giant breeds sometimes not cycling until 18 months to two years. The AKC says toy breeds may come into heat as early as four to five months, while Great Danes and large sighthounds may wait until about two years.

Early cycles can be irregular. VCA notes that young dogs can cycle erratically for up to two years, and the AKC mentions split heats, where estrus pauses and resumes a few weeks later. Frequency also varies, with small breeds sometimes cycling three times a year and giant breeds once. If your dog is well past two years old and has never been in heat, or her cycles are suddenly very erratic, mention it at your next vet visit.

Signs your dog is in heat

The earliest sign is vulvar swelling, which is not always noticeable. Bloody discharge is often what owners spot first, and it typically becomes watery and pink as she moves into estrus. She may also urinate more often or leave small marks, which attracts males. During estrus, many females hold the tail to one side, called flagging.

Behavior changes too. The AKC says some dogs become withdrawn, others overly friendly or irritable with other dogs. Small dogs can have silent heats with little visible swelling or discharge, so a male dog's sudden interest is sometimes the first clue. Keep a calendar of start dates and how long each heat lasts, because that record is useful to your vet.

How to care for her at home

Keep a steady routine, offer comfort when she seeks it and give her space when she wants it. The AKC found no evidence that dogs suffer menstrual-type cramps. If discharge bothers you, doggy diapers or covers protect furniture and floors, and our dog diapers collection is a place to look for sizes. Change them often and wash the area gently to keep skin clean.

Keep her cool, hydrated and gently exercised, and expect her to be more distractible. Watch for scratching or licking at the area, which can mean irritation. Wash bedding on a regular schedule. Do not bathe or groom her in any way your vet has not approved if she seems sore, and call your vet before using any product on the genital area.

Keeping her safe from unplanned pregnancy

Pregnancy is possible at any point during estrus, because sperm can survive about a week, and it can happen without a visible tie. Gestation lasts about 63 days. The AKC is blunt that a leash is the most effective protection: keep an unspayed female on a leash at all times, and do not leave her tied outside, since males can follow her scent to the yard even if it is fenced.

Diapers do not prevent pregnancy. Skip off-leash parks and dog daycare until the heat is finished. If she is accidentally mated, call your vet as soon as possible. The AKC notes that mismate injections vary in safety and success and are not a reliable fix, so this is a decision to make with your vet. Ending a pregnancy with medication carries risks.

Pyometra, spaying and when to call the vet

Know one serious risk. Pyometra is a rare but life-threatening uterine infection that usually appears four weeks to four months after a heat, and it is more likely in older dogs. Warning signs include increased thirst and urination, a change in appetite and low energy, and the AKC says that spaying a dog with pyometra costs four to five times more and is more dangerous than spaying a healthy young female. Call your vet the same day if you see these signs.

Spaying before the first cycle is the best way to prevent pregnancy, and VCA says most vets suggest spaying before six or seven months, though some large breeds may benefit from waiting until after the first cycle. Ask your vet what suits your dog, and see our page on what spay and neuter surgery costs.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.