Dog Heat Cycle: How Long It Lasts & How Often
Most female dogs come into heat about every 7 months (normal range 4–13 months), and the visible heat, proestrus plus estrus, lasts about two to three weeks. Figures from the Merck Veterinary Manual, VCA and Cornell.
| Question | Typical answer | Source |
|---|---|---|
| How often do dogs go into heat? | Usually twice a year; average interval 7 months, range 4–13. Some large breeds cycle every 9–12 months. | Merck |
| How long is a dog in heat? | Proestrus about 9 days plus estrus about 9 days on average, so roughly 2–3 weeks of visible heat. | Merck |
| How long does the receptive period last? | Generally about 9 days, but anywhere from 2 to 24 days. | VCA |
| When is the first heat? | Around 6 months on average; small breeds earlier, large and giant breeds as late as 18–24 months. | VCA |
Step through the four stages
What owners call "in heat" is only the first two of four stages. Tap a stage to see what's happening inside and what you'd notice.
Proestrus · about 9 days (2 days–3 weeks)
Inside: Estrogen from the ovaries rises and peaks one to two days before estrus (Cornell).
What you'll notice
Swollen vulva and bloody discharge. Males are drawn to her but she won't accept mating yet (Merck).
Bar widths use average lengths (proestrus 9 days, estrus 9 days, diestrus about 60 days, anestrus shown at about 3 months). Sources: Merck Veterinary Manual; Cornell Riney Canine Health Center.
Signs a dog is in heat
According to VCA, bloody discharge is usually the first sign owners notice, though it can go unnoticed for a few days. The discharge starts very bloody and thins to watery and pink as the days pass. She may urinate more often or mark on walks, and males will be interested in her from a long way off.
Is she fertile? Why timing needs a vet
Ovulation happens during estrus, about 2–3 days after the LH peak (Merck). Because stage lengths vary so much from dog to dog, counting days isn't enough when you're breeding. Vets run blood or vaginal tests, often every two days, and recommend the breeding days from the results (Merck).
First heat and spaying
Small breeds tend to have their first heat earlier, while large and giant breeds may not start until 18 months to 2 years (VCA). If she's already in heat and a spay is planned, Cornell's Riney Canine Health Center suggests waiting about two months after the cycle so hormones return to baseline. Talk through timing with your vet.
Log her seasons in the dog heat cycle tracker to predict the next one from her own history.
A heat that lasts much longer than usual, discharge outside of heat, or a sick, off-colour dog in the weeks after a season should be checked by a vet.
Questions breeders ask
How often do dogs go into heat?
About twice a year on average. Merck gives an average interval of 7 months with a normal range of 4–13 months.
How long is a dog in heat?
Usually two to three weeks of visible heat: proestrus about 9 days and estrus about 9 days on average (Merck).
How long does a dog bleed in heat?
Discharge is typical through proestrus and often into estrus, becoming thinner and pinker as it goes on (VCA). The length varies from dog to dog.
Can a dog get pregnant when not in heat?
Dogs ovulate during estrus, so conception happens around the heat. Because stage lengths vary widely, treat her as able to conceive from the first sign of heat until it has completely finished.
At what age do dogs stop going into heat?
Britannica notes that dogs of both sexes stay fertile well into old age, so an unspayed female can keep cycling as she gets older. If her cycles change or stop, ask your vet.