How Long Is a Dog in Heat?
Short answer: a dog's heat (estrus cycle) usually lasts about 2 to 3 weeks, and most dogs come into heat about twice a year. She can get pregnant for several days in the middle of it, roughly from day 9 to day 14, but this varies a lot between dogs.
The four stages
| Stage | How long | What happens |
|---|---|---|
| Proestrus | about 9 days (3-17) | Swollen vulva, bloody discharge, attracts males but will not accept them |
| Estrus | about 9 days (3-21) | Discharge becomes lighter, she accepts a male; ovulation happens early in this stage |
| Diestrus | about 2 months | Pregnancy, or the body returns to normal (false pregnancy can happen) |
| Anestrus | about 4 months | Rest phase until the next heat |
The "heat" owners notice is proestrus plus estrus: about 18 days on average, often 2 to 3 weeks.
How often do dogs go into heat?
- Most dogs: about every 6 months.
- Small breeds: sometimes 3 times a year.
- Giant breeds: often only every 12 to 18 months.
When is the first heat?
Usually at 6 to 12 months for small and medium breeds, and later for large and giant breeds, sometimes up to 18 to 24 months. The first heat can be shorter or irregular.
Signs your dog is in heat
- Swollen vulva and bloody or straw-colored discharge.
- Licking the area more, peeing more often.
- Restless or clingy behavior; male dogs suddenly very interested.
- In estrus, moving the tail to the side ("flagging").
Can she get pregnant?
Yes, during estrus, and sperm can survive several days, so mating late in proestrus can also lead to puppies. If she was bred, the due date is about 63 days after ovulation, usually 58 to 68 days after the first mating: use the calculator below. To prevent pregnancy, keep her strictly separated from intact males for the whole heat and talk to your vet about spaying.
Sources: Merck Veterinary Manual (reproductive cycle of the bitch); American Kennel Club.
Try the dog pregnancy calculator
Enter your own numbers below, or open the full dog pregnancy calculator with the formula and more examples.
This guide is general information, not veterinary advice. Your pet may differ: ask your vet. Terms
Frequently asked questions
How long does a dog bleed in heat?
Bloody discharge usually lasts about 7 to 10 days (proestrus) and then lightens during estrus.
How many times a year does a dog go into heat?
Most dogs about twice a year; small breeds may cycle three times and giant breeds once a year or less.
When can a dog get pregnant during heat?
During estrus, usually around the middle of the heat (often days 9 to 14), but it varies: progesterone tests by a vet show the real timing.
Can a dog be spayed while in heat?
It is possible but riskier because of increased blood flow; many vets prefer to wait 2 to 3 months after the heat.