How Long Is a Dog in Heat? Dog Heat Cycle Stages, Signs and When to Breed

A dog is usually in heat for about two to three weeks. The bleeding stage (proestrus) lasts about 9 days on average and the receptive stage (estrus) about another 9, but the Merck Veterinary Manual gives normal ranges of 2 days to 3 weeks for the first and 3 days to 3 weeks for the second. Most female dogs come into heat about twice a year, roughly every 7 months, though anything from 4 to 13 months between cycles can be normal.

If your dog is a pet and you are not planning a litter, the most useful thing to know is that the American Animal Hospital Association recommends spaying every dog not intended for deliberate breeding, and your veterinarian can tell you the right age for her size. If you are planning a litter, the timing of the actual breeding belongs with your veterinarian too, because the fertile days inside a heat cannot be read reliably from her behavior. Once a breeding happens, the free Creatures dog gestation calculator turns the date into a whelping window, no account needed.

This guide covers the four stages of the cycle, the signs of each, when the first heat happens, how to manage a dog in heat, the spay decision, a heat-related emergency every owner of an unspayed dog should know, and how breeders and their vets time a breeding.

The four stages of the dog heat cycle

Veterinarians divide the cycle into four stages. Only the first two are what owners call “heat”. The descriptions below follow the Merck owner chapter and the professional chapter on breeding management of female dogs.

• Proestrus, about 9 days (2 days to 3 weeks): bloody discharge and a swollen, firm vulva; males are interested, but she will not let them mate.
• Estrus, about 9 days (3 days to 3 weeks): she accepts a male; the discharge may lessen and turn straw colored, and the vulva softens.
• Diestrus, about 2 months if she is not pregnant: she refuses males again; the discharge fades and the vulva slowly shrinks.
• Anestrus, 1 to 6 months: no signs; the resting phase before the next heat.

Proestrus: the start of heat

Proestrus is the stage most owners notice first. Her vulva swells and becomes firm, and there is a bloody discharge from the vagina. Male dogs find her attractive, but she does not yet allow them to mount, and the professional chapter notes she may become more playful. Estrogen rises through this stage.

The discharge is easy to miss in a dog that cleans herself often, and the professional chapter warns that even an observant owner may not notice the true start of proestrus for a few days. So if you are counting days, treat your “day 1” as approximate.

Estrus: the receptive stage

During estrus she will accept a male. Estrogen is falling and progesterone is rising. The discharge varies between dogs: it may lessen and become straw colored, or stay red. The vulva becomes soft. Ovulation happens in this stage, about 2 to 3 days after a hormone surge called the LH (luteinizing hormone) peak, and dogs ovulate whether or not they are bred.

The important point for both pet owners and breeders: she can be receptive for days, and the professional chapter states that estrus behavior “may not coincide precisely with the fertile period”. A dog that has stopped bleeding is not necessarily past the point where she can conceive.

Diestrus and anestrus

In diestrus she refuses males again, the discharge fades and the swelling slowly goes down. Progesterone stays high for weeks whether or not she is pregnant, and in a dog that is not pregnant diestrus usually lasts about 2 months. Anestrus is the quiet stage that follows, lasting 1 to 6 months, before the next proestrus begins.

How often dogs come into heat, and when the first heat happens

Merck’s owner chapter says female dogs usually cycle twice a year. The gap between cycles can range from 4 to 13 months, with an average of 7, and some large breeds such as Great Danes may cycle normally only every 9 to 12 months.

The first heat marks puberty. Merck’s chapter on reproductive management of the female dog puts the typical age at 10 to 12 months, with a range of 6 to 24 months, and says large and giant breeds come into heat later than small breeds. AAHA’s 2019 canine life stage guidelines give an even wider spread: from about 4 months in some small breeds to 24 months in some large breeds. That is why a small-breed puppy can surprise a new owner well before her first birthday.

A growing puppy’s size is the best clue to which end of that range she will fall at, and our puppy weight chart guide explains how small, medium and large breeds grow at different speeds.

Living with a dog in heat

For a pet you do not plan to breed, the goal during a heat is simple: keep her away from intact males for the whole of proestrus and estrus, and remember that the receptive days can come after the bleeding seems to stop.

Practical steps owners use:

• Leash every walk, and supervise every minute outdoors. A fence that keeps her in will not always keep a determined male out.
• Walk at quieter times and places, away from dog parks and daycare, until the cycle is over.
• Keep intact males in the household separate, in a different room or with a trusted friend, rather than relying on watching them.
• Protect your furniture with washable covers or fitted dog heat pants, and keep her clean. Heat pants are for mess, not contraception.
• Write down the dates. The first day of bleeding and the day the swelling goes down tell your vet a lot, and they help you predict the next heat.

If she mates by accident

Call your veterinarian promptly. Merck notes that pregnancy can be ended by a veterinarian with medication, and that the pregnancy should be confirmed first, because 60 percent of dogs that are mated by mistake do not become pregnant. Your vet will explain the options and their risks for your dog. Do not give her any medication at home.

If she does become pregnant, our guide to how long dogs are pregnant explains the due date and the whelping signs, and the dog gestation calculator gives the whelping window from the mating date.

The spay decision for pets

AAHA’s 2019 canine life stage guidelines recommend that all dogs not intended for deliberate breeding be spayed or castrated, and note that sterilized dogs of both sexes live longer on average than intact dogs. For a pet, that is the default this guide recommends too: spaying ends heat cycles, unplanned litters and the uterine infection described in the next section.

Timing is a conversation for your veterinarian, and AAHA’s proposed ages for sterilization explain why it depends on size:

• Dogs expected to weigh under 45 pounds as adults: generally spayed by 5 to 6 months, before the first heat. AAHA says spaying before the first estrus minimizes the risk of mammary (breast) cancer, and that the risk rises with the number of heat cycles up to 2.5 years of age.
• Females expected to weigh 45 pounds or more: AAHA calls the evidence less clear and gives a range of about 5 to 15 months, waiting for growth to stop in many cases. It asks vets to balance the lower mammary cancer risk and fewer unwanted litters of an earlier spay against a lower risk of some orthopedic problems, some cancers and urinary incontinence with a later one.

AAHA is also candid that the research shows associations rather than proof of cause, and that results in one breed may not apply to another. Merck’s professional chapter makes the same point: there is no consensus on the single best age to spay, so each dog and family should be considered individually. Your vet knows your dog’s breed, expected size and lifestyle, which is why the decision belongs with them.

Pyometra: the heat-related emergency

Pyometra is a bacterial infection of the uterus in unspayed dogs. Merck’s owner chapter on reproductive disorders of female dogs says it is reported mainly in dogs over 5 years old and tends to occur 4 to 6 weeks after a heat. After every heat, progesterone stays high and thickens the lining of the uterus; over several cycles without a pregnancy, that lining can form cysts and fluid that bacteria infect.

The signs Merck lists:

• Tiredness and a poor appetite
• Drinking and urinating more than usual
• Vomiting
• A discharge of pus, often bloody, from the vulva, if the cervix is open
• A swollen belly with no discharge at all, if the cervix is closed

Merck warns that the signs can progress rapidly to shock and death. If an unspayed dog shows these signs in the weeks after a heat, call a veterinarian now. A closed-cervix pyometra gives no discharge to warn you, and Merck notes that treating it without surgery carries more risk because the infected uterus may burst.

When to breed a dog: how breeders and vets time it

If you are planning a litter, plan it with your veterinarian before she comes into season. Merck’s owner chapter advises exactly that: discuss the breeding with your vet ahead of time, then call as soon as you see the first signs of heat (discharge, vulvar swelling or interest from males).

Why you cannot just count days

Counting from the first day of bleeding is a poor guide, for three reasons in the Merck chapters. The first day of proestrus is often missed. Proestrus itself can last anywhere from 2 days to 3 weeks. And the fertile window sits after ovulation, which follows the LH peak by 2 to 3 days, with the eggs needing another 2 to 3 days to mature before they can be fertilized. Two dogs that started bleeding on the same day can be fertile a week apart.

What progesterone testing does

To find the fertile days, veterinarians track her hormones. Merck describes three tools, usually used together:

• Vaginal cytology: a swab of cells that shows how far into the heat she is and when hormone testing should start.
• Progesterone blood tests: typically every other day. Progesterone begins rising at about the time of the LH surge, so the day it first rises gives the vet a reference point to plan the breeding days from, and a later test confirms that ovulation happened.
• LH testing: daily, when more precision is needed, for example with chilled or frozen semen.

Merck notes that no single progesterone number marks a stage of the cycle, and that results from different laboratories or test kits are not comparable, so stick with one method through the cycle. That is the reason the interpretation belongs to your veterinarian: the useful information is the pattern across several tests, read alongside the cytology and the dog in front of them. The vet then recommends the days to breed, which also differ for natural breeding, fresh, chilled or frozen semen.

Merck’s chapter on reproductive management of the female dog adds a point that surprises many first-time breeders: the “tie” during a natural mating is not needed for conception and does not show the mating worked.

Before you breed at all

A heat is not a reason to breed. Before a planned litter, breeders usually line up:

• Health screening for both parents appropriate to the breed, with results in hand.
• Registration rules. If you want to register the puppies, the AKC’s rules set minimum and maximum ages for the dam and sire at mating and require the litter to be registered first. Our guide to AKC registration explains litter registration and the full versus limited choice.
• The pairing. A pedigree check and, in a small breed, the inbreeding coefficient. The coefficient of inbreeding guide and the free dog pedigree chart maker help, and our stud fees guide covers the contract with the stud owner.
• Homes. A plan for every puppy before the mating, not after. Our guide to finding puppy buyers covers screening.

For a breed-specific example of the health tests a parent club asks for, see the Russian Tsvetnaya Bolonka guide, and the dog breeds on Creatures page links every breed guide we have.

After the breeding: the due date

Merck’s owner chapter puts dog pregnancy at about 62 to 64 days, and its professional chapter counts 64 to 66 days from the LH peak when ovulation was timed. The dog gestation calculator adds 63 days to a breeding date and shows a deliberately broad window of 58 to 72 days, because the breeding date is rarely the conception date. If your vet timed ovulation, use their date. Our full guide to how long dogs are pregnant covers the week-by-week timeline and the whelping signs.

How to track heats and breedings on Creatures

Heat dates are easy to forget by the next cycle, and a breeding plan needs several dates kept straight. Creatures gives you a free calculator and a free account to keep the record.

1. Get a due date, no account needed. Enter the breeding date in the dog gestation calculator, or choose Exposure Window if she was with the male over several days. It returns the 63-day estimate and the window, with buttons to copy, print or add the dates to your calendar. Using the gestation calculator explains the options.

2. Give her a profile and log each heat. Add your dog and note the first day of bleeding and the end of each heat as a Breeding & Reproduction record with Track as breeding cycle turned off, which keeps it as a plain dated note. Save progesterone or other results from your vet as test result records with the lab report attached. After two or three cycles, you can see her own interval instead of guessing from averages.

3. Record the breeding. Add a Breeding & Reproduction record, keep Track as breeding cycle on, name the sire (a dog on Creatures, or just a name you type) and enter the date, or a date range for several days together. If your vet gave you a due date from ovulation timing, enter it in Projected date override rather than changing the breeding date. The steps are in recording a breeding.

4. Follow it. Her Breeding tab shows the pregnancy with her due date, window and what to expect, and Creatures schedules a due-date reminder. The Breeding dashboard lists every expecting female, with Due soon and Overdue flags. If she comes back into heat, She came back into heat ends that breeding; see when a breeding doesn’t take.

5. Record the litter. When the puppies arrive, record the birth with the numbers born alive and stillborn, and create the puppies’ profiles now or later, already linked to their mother. See recording births and creating a litter. The puppies’ weights then go on their own profiles, which is where our puppy weight chart guide picks up.

For pet owners, the same profile is a good home for the spay date and the follow-up visits, with reminders for anything your vet wants rechecked.

Frequently asked questions

How long is a dog in heat?

Usually about two to three weeks in total. Merck gives about 9 days for proestrus (range 2 days to 3 weeks) and about 9 days for estrus (range 3 days to 3 weeks).

How often do dogs go into heat?

Most dogs cycle about twice a year. Merck gives an interval of 4 to 13 months, 7 on average, and some large breeds, such as Great Danes, cycle only every 9 to 12 months.

When does a puppy have her first heat?

Typically at 10 to 12 months, with a range of 6 to 24 months (Merck). AAHA notes it can be as early as 4 months in some small breeds; large breeds tend to be later.

Can a dog get pregnant when she is not bleeding?

Yes. The receptive stage often comes as the discharge lessens or turns straw colored, and the fertile days do not line up exactly with her behavior. Keep her away from intact males until the whole heat is over.

Should I let my dog have one heat before spaying?

For a dog expected to weigh under 45 pounds, AAHA recommends spaying before the first heat, at about 5 to 6 months, partly because mammary cancer risk rises with each heat. For larger dogs the evidence is less clear, and AAHA leaves the timing to you and your veterinarian.

How do I know the best day to breed my dog?

Ask your veterinarian to time ovulation. Merck describes vaginal cytology plus progesterone tests every other day, and LH tests in some cases; the vet reads the pattern and recommends the breeding days.

Do this next on Creatures

Tracking a heat, planning a litter or keeping a pet’s spay records, these are the next steps on Creatures.