A dog’s season, or heat, is the part of her reproductive cycle when she can become pregnant. Knowing how long it lasts and how often it comes back helps you plan walks, avoid an unplanned litter and notice anything unusual. This guide covers how long a dog stays in heat, the four stages of the dog heat cycle, how often it happens, how to look after her during a season and when to speak to your vet.
How long does a heat last?
For most dogs the visible heat, made up of the proestrus and estrus stages, lasts about 2 to 3 weeks. Each stage is about 9 days on average, but individual dogs vary, and sources give slightly different ranges:
| Stage | Typical length | Source note |
|---|---|---|
| Proestrus | About 9 days | Merck: range 2 days to 3 weeks; Cornell: about 6 to 11 days |
| Estrus | About 9 days | Merck table: about 5 to 10 days |
| Proestrus + estrus | About 2 to 3 weeks | The usual “heat” you see |
Because the ranges differ between dogs and between sources, treat the numbers as a guide and track your own dog’s pattern. If you want the shortest accurate answer: a dog is in heat for about two to three weeks, and the whole cycle, including the resting phase, takes months.
The four stages of the dog heat cycle
- Proestrus. The vulva swells and there is a bloody discharge. She attracts males but usually refuses to mate.
- Estrus. She is receptive. The discharge often becomes thinner and straw-coloured. This is when she can become pregnant, and ovulation happens during it.
- Diestrus. The weeks after estrus when she is either pregnant or resting.
- Anestrus. A resting phase between cycles, usually a few months, before the next proestrus.
Dates are hard to pinpoint by eye alone. Breeders who need exact timing use progesterone tests with their vet.
What each stage looks and feels like
Understanding behaviour makes it much easier to manage a season at home.
| Stage | What you may see | What to do |
|---|---|---|
| Proestrus | Swollen vulva, bloody discharge, males show interest, she may be restless or more clingy | Start extra supervision; keep her on a lead |
| Estrus | Discharge often paler, she may stand for males, tail moves to the side | Highest risk of mating; no unsupervised time outdoors |
| Diestrus | Swelling goes down, discharge stops, she loses interest in males | Watch for signs of illness; if mated, follow pregnancy dates |
| Anestrus | Nothing visible | Normal routine; a good time to plan with your vet |
Every dog is a little different. One dog may bleed heavily and another very little, and some are quiet while others are noticeably moody. Notice what is normal for her, because that is what you will compare against next time.
How often do dogs come into heat?
On average about every 7 months, with a range of 4 to 12 months between heats. Small breeds often cycle more often than giant breeds, and a first heat can come anywhere from around 6 months to about 2 years, depending on the dog and her size. Concannon’s review of the canine cycle describes the long, variable resting phase as the main reason interval lengths differ between dogs.
The pattern is individual, so after two or three cycles you can usually predict your own dog within a few weeks. A dog who has had one heat 6 months after the last and another 8 months after that is simply showing you her range.
Your dog’s first heat
A first heat can surprise owners because it is often shorter, lighter or less regular than later ones. Smaller dogs tend to come into season earlier and larger breeds later, sometimes not until closer to 2 years. If you do not know your dog’s age exactly, the Dog Age Calculator shows her life stage, which is a better guide to whether a first heat is due than the number of months alone. If she has not had a heat by 2 years, speak to your vet.
A worked example
A dog whose last heat started on 1 September 2026 and who usually cycles every 7 months is expected to start her next heat around 1 April 2027, with proestrus ending around 10 April and estrus around 19 April, using the average lengths above. If she cycles every 6 months, the next heat is around 1 March 2027; every 12 months, 1 September 2027.
| Her usual interval | Next heat starts around |
|---|---|
| 6 months | 1 March 2027 |
| 7 months | 1 April 2027 |
| 12 months | 1 September 2027 |
Use your own dates in the Dog Heat Cycle Calculator. The result is an estimate; cycle length varies between dogs and breeds, so start watching a week or two earlier than the predicted date.
Caring for a dog in heat
- Keep her on a lead and in a secure garden. Males can detect a female in heat from a distance, so check gates and fences.
- Avoid leaving her unsupervised outside, and take extra care at the dog park or on walks.
- Wash bedding often and use a washable blanket where she rests. Dog-specific pants are an option if you wish to manage discharge indoors.
- Keep her routine as normal as possible. Gentle exercise and play are fine unless your vet says otherwise.
- Do not scold her for licking herself or for mood changes; both are part of the cycle.
- Ask your vet if you have questions about anything unusual.
Dog heat and the crate or bed
Dogs in heat can be restless, and some owners want a safe, washable place for them to rest. If you use a crate, check that it is the right size so she can stand, turn and lie down comfortably; our guide to what size crate your dog needs explains how to measure. A crate is a resting place, not a place to confine her for long periods.
Preventing an unplanned litter
If you have no plans to breed, the most reliable protection is to keep her away from intact males throughout the whole heat, not only during the days she seems most interested. Remember that she may be fertile for most of the 2 to 3 weeks, and that males can be persistent. Many owners also discuss neutering with their vet; the timing and the decision are individual and depend on her size, breed and health.
If she may be pregnant
If your dog was with a male during heat, you can estimate the due date from the mating date. Use the Dog Pregnancy Due Date Calculator or the Dog Pregnancy Week Calculator, and read our guide to how long dogs are pregnant for the full timeline. Ask your vet to confirm the pregnancy, since you cannot tell from how she looks.
Signs a heat is not normal
Speak to your vet if:
- She has no heat by 2 years of age.
- A heat lasts more than 4 weeks.
- She has a discharge and seems unwell after a heat. This can be a sign of a womb infection called pyometra, which is urgent.
- Her cycle suddenly changes, for example very frequent or very rare heats.
- She is drinking much more than usual, vomiting or off her food in the weeks after a season.
If you notice signs of illness after a season, do not wait: contact your vet or an emergency clinic.
Heat cycle myths
- “A dog should have one litter before she is spayed.” There is no veterinary reason that a dog needs to have a litter or a heat first. Ask your vet about the best timing for your dog.
- “Dogs bleed for the whole three weeks.” Discharge changes during the heat and may lessen or change colour during estrus.
- “Dogs in heat should not be walked.” Most dogs can be walked, but keep them on a lead and avoid busy places where males are likely to be.
- “The cycle is always exactly the same.” Heats can vary by a few weeks, especially in young dogs.
- “She is only fertile on one day.” The fertile window is several days, and sperm can survive for days, so do not rely on a single date.
How to track your dog’s cycle
Write down the date each heat starts and how many days the discharge and swelling last. After two or three cycles you will see a pattern. A simple record has these columns:
| Heat number | Start date | Days of swelling and discharge | Notes |
|---|---|---|---|
| 1 | First heat, age at start | ||
| 2 | Anything unusual | ||
| 3 | Compare with earlier heats |
Put the latest start date into the Dog Heat Cycle Calculator with her usual interval in months to get an estimated next date, and keep a note of anything unusual to show your vet.
Cats have heat too, but it works differently
Cats are not in heat for a fixed 2 to 3 weeks and then resting for months. Queens cycle repeatedly through the breeding season and ovulate in response to mating, which is why their pregnancy dates are easier to count from the mating day. If you share a home with both species, our guide to how long cats are pregnant explains the difference.
Questions to ask your vet
- At what age should I expect her first heat, given her size and breed?
- How long should her heat last, and what discharge is normal?
- How should I keep her safe and comfortable during a season?
- What are the options and the right timing if I do not want her to have puppies?
- Which signs after a heat mean I should call you straight away?
Heat in small, medium and large dogs
Size changes the rhythm of the cycle. Small breeds tend to come into their first heat earlier and cycle more often, while giant breeds start later and may have longer gaps. That is why the average of about 7 months hides a wide spread, and why a 4-month gap in a small dog and a 12-month gap in a giant dog can both be normal. If you are not sure whether your dog’s pattern is normal, write down her heat dates for a year and show your vet.
| Dog size | What is often seen |
|---|---|
| Small | Earlier first heat, shorter gaps between heats |
| Medium | Close to the average of about 7 months |
| Large and giant | Later first heat, sometimes longer gaps |
These are tendencies, not rules; use your own dog’s record to plan.
Seasonal planning: what to do before and after
A little planning makes a season much easier to manage.
Before the heat is due: check your garden fence and gate, make sure her microchip details are current, stock up on washable bedding and decide who will walk her. If you plan to travel or board her, tell the kennel in advance because many do not accept dogs in season.
During the heat: stay with her outside, avoid places where off-lead dogs run freely, and keep walks short and on a lead. Some owners walk at quieter times of day.
After the heat: the weeks following a season are when to watch for signs of illness. Keep her routine normal, note the date the swelling went down, and add the heat to your record.
Training and behaviour during a season
Hormones can change a dog’s mood. Some become more affectionate, others irritable or distractible, and recall can be less reliable. Use a lead, keep training sessions short and positive, and avoid correcting behaviour that is clearly hormonal. If her behaviour changes in a way that worries you, ask your vet or a qualified trainer.
Reading this in the US, UK, Australia or Canada
The 2 to 3 week heat and the roughly 7 month interval are used by vets in every country. The local differences are around words and rules. The UK and Australia often say “in season” where the US and Canada say “in heat”, and “neutering” where North America says “spaying”. Councils and landlords in some areas have rules for dogs in season, for example in dog parks, training classes or boarding kennels, so check with your local council or kennel before you book anything. If you travel, remember that a season can start earlier or later than the calculator predicts, so build in a little slack.
Quick summary
- A heat (proestrus plus estrus) usually lasts about 2 to 3 weeks.
- Dogs come into heat about every 7 months, with a range of 4 to 12 months.
- Keep her on a lead and supervised throughout; she may be fertile for much of the heat.
- Write down each start date; after two or three cycles you can predict the next one.
- Call your vet for no heat by 2 years, a heat longer than 4 weeks, or illness after a season.
- Use the Dog Heat Cycle Calculator to estimate the next heat.
Frequently asked questions
How long does a dog stay in heat?
Proestrus and estrus together usually last about 2 to 3 weeks.
How often do dogs go into heat?
About every 7 months on average, with a range of 4 to 12 months. Small breeds often cycle more often than giants.
When is a dog fertile?
During estrus. Timing varies, so breeders use progesterone tests with their vet.
How long is proestrus?
About 9 days on average. The Merck Veterinary Manual gives a range of 2 days to 3 weeks for individual dogs.
What are the signs of heat?
Vulval swelling and bloody discharge in proestrus, and a discharge that often thins and turns straw-coloured when she is receptive in estrus.
When should I talk to the vet about heat?
If there is no heat by 2 years of age, if a heat lasts more than 4 weeks, or if she is unwell with a discharge after a heat, which can be urgent.
Can I walk my dog while she is in heat?
Most dogs can be walked, but keep her on a lead, avoid busy dog areas and never leave her unsupervised outside.
Sources
- Merck Veterinary Manual (pet owner version) — Management of Reproduction in Dogs
- Concannon P.W. (2011) Reproductive cycles of the domestic bitch. Animal Reproduction Science 124:200–210
- Cornell University College of Veterinary Medicine — Dog estrous cycles
Related calculators
- Dog Heat Cycle CalculatorPredict your dog's next season and the stages of the heat cycle.
- Dog Pregnancy Due Date CalculatorEstimate your dog's due date and the normal whelping window.
- Dog Pregnancy Week CalculatorSee which day and week of pregnancy your dog is in, counted from the mating date, and how many days remain.
- Dog Age CalculatorConvert your dog's age into human years, taking size into account.
Keep reading
- How Long Are Dogs Pregnant? Timeline and Due Date GuideDog pregnancy lasts about 63 days from ovulation and 58 to 68 days from mating. Learn how to count, what is normal and when to call the vet.
- What Size Crate Does My Dog Need? A Measuring GuideMeasure your dog's length and height, add 5 to 10 cm (2 to 4 in) and match the result to the crate maker's inside measurements. Includes examples and puppy tips.