Dog Heat Cycle: How Long Are Dogs in Heat?

A heat lasts 2 to 3 weeks in most dogs, and some run far longer. Most dogs come into heat about twice a year. Enter the first day you saw blood and the tracker shows the average stage she is in, when the next season is due, and the warning signs to watch for afterwards. It will not give you "safe days", because there are none.

How long is a dog in heat?

The visible part, swelling and bleeding and male attention, runs about 2 to 3 weeks. The full cycle is longer, because it continues invisibly for another two months after the interesting part stops.

The ranges matter more than the averages. A 9 day average hides dogs that run 3 days and dogs that run 21, which is exactly why people get caught out by an unplanned litter.

How often do dogs go into heat?

Roughly twice a year. The interval between cycles runs from 4 to 13 months and averages about 7.

A common myth is that size predicts this. It does not. Size predicts the age of her first season, but not the gap between later ones: published figures put German Shepherds at a shorter average interval than Dachshunds. Basenjis and some sled dog breeds genuinely do cycle once a year, but that is a breed trait rather than a size rule.

The first year or two is often irregular, with a short cycle followed by a long gap. That settles with maturity. A dog who suddenly changes her established pattern is worth a vet visit.

When is a dog fertile?

The textbook answer is that she will not accept a male until around day 7 to 10 and that most dogs ovulate around day 11, which is where the “days 10 to 14” breeding window comes from. Treating that as a calendar is how litters happen.

Ovulation can occur anywhere from about day 3 to day 18. She is fertile from a couple of days before ovulation until about 5 days after it, and sperm survive for days inside her, so a mating in what looks like early proestrus can still produce puppies. A dog whose proestrus lasts only 3 days is standing and ovulating while the calendar still says “bleeding stage”.

There are no safe days to point at. If you are not breeding, assume she is fertile for the whole season. If you are, your vet times ovulation with progesterone tests, because that is the only thing that actually identifies it.

Signs your dog is in heat

• swollen vulva, often the first sign
• bloody discharge, turning lighter and pinker as the cycle moves on
• licking the area more than usual
• urinating more often, and in more places, which is scent marking
• male dogs appearing at your gate
• flagging: holding her tail to one side when touched near the base
• behaviour changes in either direction, clingy or withdrawn or snappy

Some dogs have a silent heat with almost no visible signs, and still get pregnant. Others have a split heat, where the cycle starts, stops and restarts weeks later.

The dangerous weeks after a heat: pyometra

It is most common in older intact bitches, and the risk never goes away while she is unspayed. Even a spayed dog can rarely develop a stump pyometra. Treat the signs below as a same-day emergency, not a wait-and-see:

• drinking and urinating noticeably more
• off her food, vomiting, or unusually flat
• passing pus-like, smelly or bloody discharge
• swollen or tender in the belly
• collapsed, weak, or showing pale gums, which suggests she is becoming septic

A dog whose cervix has closed shows no discharge at all, and that is the more dangerous version, not the reassuring one: the pus has nowhere to go, the uterus can rupture, and she becomes severely ill very quickly. Treatment is usually emergency surgery. Antibiotics alone do not fix it.

Looking after a dog in heat

• Lead walks only, until the swelling and discharge have completely gone and she rejects males again. That can be longer than three weeks, since proestrus and estrus can each run up to 21 days.
• Supervise the garden. Determined males get through fences, and a tie can happen in under a minute.
• Separate intact males properly. A closed door is not separation when both dogs are motivated.
• Dog pants or a washable bed cover save your floors. Most dogs keep themselves fairly clean.
• Expect mood changes and give her somewhere quiet to retreat to.
• She can conceive to a second male days after the first, so one accident is not a reason to relax the rules.

If an accidental mating happens

Never try to pull a tied pair apart. You can injure both dogs badly, and it will not prevent anything. Let them separate naturally, then phone your vet.

What can be done depends on where you live and how long ago it was:

• Spaying ends the pregnancy and prevents future ones.
• Aglepristone, given as two injections 24 hours apart, can be used up to day 45 after mating and works best when given early, so do not wait. It is widely used in the UK and Europe, but it is not licensed in the US or Canada.
• Older estrogen “mismate” injections carry a real risk of pyometra and bone marrow suppression, so vets rarely recommend them now.
• An ultrasound at about day 25 confirms whether she is actually pregnant, so you are not treating a pregnancy that does not exist.

When bleeding is not a heat

This tracker assumes a normal season in an intact, adult dog. Call your vet rather than tracking if:

• she is spayed and bleeding, which can mean an ovarian remnant, a tumour, or a stump pyometra
• she is a senior with new bleeding
• she is under about 4 months old
• bleeding goes on longer than 3 weeks
• signs of heat continue past about 40 days, which can mean a follicular cyst or an ovarian tumour keeping oestrogen high, and prolonged high oestrogen damages bone marrow
• she has never had a season by 24 months

Urinary infections, injuries, clotting disorders and tumours can all look like a season to an owner.

Spaying and the heat cycle

Vets do not usually spay during a heat, for a practical surgical reason rather than a rule: the blood supply to the reproductive tract increases enormously during a season, so there is more bleeding and more risk. Most practices advise waiting two to three months. The exception is pyometra, where surgery happens when it is needed, regardless of timing.

When to spay in the first place is a genuine debate, not a settled one: timing affects orthopaedic and cancer risks differently in different breeds and sizes, so it is worth a specific conversation with your vet about your dog rather than a rule of thumb from the internet.

Frequently asked questions

Where these numbers come from

• Stage lengths and cycle frequency: the American Kennel Club’s How Long Are Dogs in Heat? (proestrus and estrus averaging 9 days each with a 3 to 21 day range, diestrus about 60 days, anestrus 4 to 6 months).
• Cycle interval: the MSD Veterinary Manual gives 4 to 13 months with an average of 7, and no size rule. VCA gives 4 to 12 months averaging 7, puberty usually at 9 to 10 months, receptive from days 7 to 10, ovulation around day 11 and possible from day 3 to day 18.
• Ending an unwanted pregnancy: the UK product information for aglepristone (Alizin), licensed for use up to 45 days after mating and most effective early.
• Prolonged heat, cysts and ovarian remnants: the Merck Veterinary Manual on reproductive disorders in female dogs.
• Pyometra timing and signs: VCA on pyometra (usually within 4 to 6 weeks of a heat, possible 2 to 16 weeks after).