Dog Heat Cycle Calculator
See which stage of heat she's in, when it should end, and when her next heat is due.
Enter her last heat
The day you first saw swelling or bleeding. Your best guess is fine.
Know it? We'll use her own rhythm instead of the average for her size.
When is her next heat?
Enter the first day of her last heat to see where she is in her cycle and when the next one is due.
How long is a dog in heat?
Most dogs are in heat for 2 to 3 weeks. The visible part of the heat has two stages, each lasting about 9 days on average according to the Merck Veterinary Manual: proestrus, when the bleeding starts, and estrus, when she is fertile and willing to mate.
Those are averages. Either stage can be as short as a few days or as long as 3 weeks, so one dog's heat might be over in 10 days while another's lasts a month. That's why the safest rule is to keep her away from unneutered males from the first sign of heat until every sign has been gone for a few days.
The 4 stages of the dog heat cycle
| Stage | How long | What you'll see |
|---|---|---|
| Proestrus | About 9 days (2 days to 3 weeks) | Swollen vulva, bloody discharge. Males are attracted, but she won't mate yet. |
| Estrus | About 9 days (3 days to 3 weeks) | Discharge often lightens. She accepts males, ovulates, and can get pregnant. |
| Diestrus | About 2 months | Heat signs fade and she refuses males. Pregnant or not, her hormones stay high. |
| Anestrus | 1 to 6 months | The resting phase between cycles, with no signs of heat. |
How often do dogs go into heat?
Most dogs come into heat about twice a year. Merck puts the average gap at 7 months, with a normal range of 4 to 13 months. Size makes a big difference:
- Small breeds often cycle every 4 to 6 months, sometimes 3 times a year.
- Medium and large breeds usually cycle every 6 to 8 months.
- Giant breeds like Great Danes may cycle only every 9 to 12 months.
Each dog tends to settle into her own rhythm once she is grown, which is why the calculator asks for the heat before her last one if you know it. Her first heat usually comes between 6 and 15 months old: earlier in small breeds, and as late as 18 months to 2 years in giant breeds.
Caring for a dog in heat
- Keep her secure: walk her on a leash, never leave her alone in the yard, and watch doors. Dogs in heat can be determined escape artists, and males will travel a long way to find her.
- Skip the dog park and daycare until the heat is fully over.
- Manage the mess: washable dog diapers or heat pants, and a towel over her favorite spots, help keep things clean. Diapers do not prevent mating.
- Be patient: some dogs get clingy, restless, or grumpy, and some eat less for a few days.
When to call the vet
Call your vet if bleeding lasts more than about 3 weeks, if heats come much more often than every 4 months, or if a grown dog hasn't had a heat in over a year and isn't spayed. Call urgently if, in the weeks after a heat, she drinks much more than usual, has a smelly or pus-like discharge, vomits, or seems lethargic. These can be signs of pyometra, a womb infection that needs treatment fast.
If she was bred, our dog pregnancy calculator gives her due date and a week-by-week plan.
Frequently asked questions
How long is a dog in heat?
Most dogs are in heat for 2 to 3 weeks. The first part, proestrus, lasts about 9 days, with swelling and bloody discharge. Then comes estrus, also about 9 days on average, when she is fertile and willing to mate. Either stage can be as short as a few days or as long as 3 weeks, so some heats run longer.
How often do dogs go into heat?
Usually about twice a year, every 7 months on average. Normal gaps range from about 4 to 13 months. Small breeds can cycle up to 3 times a year, while giant breeds like Great Danes may cycle only every 9 to 12 months. Each dog tends to keep her own fairly regular rhythm once she is grown.
When does a dog have her first heat?
Most dogs have their first heat between 6 and 15 months old. Small breeds can start as early as 4 to 6 months, while large and giant breeds may not cycle until 18 months to 2 years. The first few cycles can be irregular.
When can a dog get pregnant during her heat?
She is most fertile during estrus, which on average starts about 9 to 10 days after the first sign of heat. But timing varies a lot between dogs, and sperm can survive for several days, so a dog can get pregnant earlier or later than average. To avoid a litter, keep her away from unneutered males for the whole heat. To plan one, ask your vet about progesterone tests.
What are the signs a dog is in heat?
A swollen vulva, bloody or pink discharge, licking her rear end more, peeing more often, and male dogs suddenly being very interested in her. Later in the heat she may flag her tail to the side and try to get out to find a mate. Some dogs have quiet heats with very few signs.
Do dogs stop going into heat when they get older?
No. Dogs don't go through menopause, so an unspayed female keeps cycling for life, although the gaps may get longer as she ages. An older unspayed dog is also at risk of pyometra, a serious womb infection that often shows up in the weeks after a heat. Call your vet urgently if she drinks a lot, has a smelly discharge, or seems unwell after a heat.
Sources
- Merck Veterinary Manual, Dog Owners version. Management of Reproduction in Dogs (stages of the heat cycle, their length, and how often dogs cycle).
- Merck Veterinary Manual. Table: Estrous (Heat) Cycle in Female Dogs.
- VCA Animal Hospitals. Estrous Cycles in Dogs (age at first heat, length of heat, signs).
- American Kennel Club. How Long Are Dogs in Heat? What to Know About Heat Cycles.
- American Kennel Club. How Often Do Dogs Go Into Heat? (cycle frequency by breed size).
- Root Kustritz MV. Managing the reproductive cycle in the bitch. Veterinary Clinics of North America: Small Animal Practice, 2012 (interestrous interval of 6 to 7 months on average, range 5 to 12).
Sources last checked: . How we calculate
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