How long is a dog in heat?
The short answer: about three weeks. The honest answer: somewhere between two and four weeks, and the same dog can vary from one heat to the next. That is why it pays to write the dates down.
The heat in numbers
What owners call “the heat” is really two stages that flow into each other:
- Proestrus: about 9 days, range 3 to 17. The vulva swells, the dog bleeds, males are interested, but she still rejects them.
- Estrus (standing heat): about 9 days, range 3 to 21. The discharge turns lighter and she accepts the male. Now she is fertile.
Together that is usually 18 to 21 days. The bleeding often stops before the heat is over; anyone who watches only the blood considers the dog “done” too early and underestimates exactly the days on which she can conceive.
Standing heat is followed by diestrus, roughly 60 to 90 days during which progesterone stays high whether she was mated or not. Nothing is visible from the outside, but hormonally the heat is only complete after this stage. Then comes anestrus, the resting phase that lasts until the next heat.
When does the first heat come?
Usually between 6 and 12 months of age. Small breeds start earlier, often at 5 to 8 months; large and giant breeds take longer, 12 to 18 months is normal, and Great Danes or wolfhounds may take up to 24 months. The first heat is often inconspicuous or irregular: a silent heat without visible signs and a split heat, where the bleeding stops after a few days and starts again two to four weeks later, are common in young dogs and usually harmless.
How often does a dog come into heat?
On average every six to seven months, so about twice a year. The range is wide and depends mainly on size:
| Size | Typical interval |
|---|---|
| Small breeds | 4 to 6 months |
| Medium breeds | 6 to 7 months |
| Large breeds | 6 to 8 months |
| Giant breeds | 8 to 12 months |
| Basenji and some primitive breeds | once a year |
An individual dog's interval is fairly stable. If you have noted the last two or three heats, you can predict the next one to within a week or two. That is exactly what Lunella does: the first time the app uses the reference value for your dog's size, after that it uses her actual intervals.
There is no menopause in dogs. They come into heat all their lives, often more irregularly and with weaker signs in old age.
When to see the vet
- Standing heat longer than three weeks, or a heat that lasts longer than four weeks in total (prolonged heat: ovarian cysts or hormone-producing tumours are possible).
- Interval shorter than four months: the uterus cannot recover.
- Interval longer than twelve months in a breed with a normal cycle, or a dog that has never been in heat by two years of age.
- Very heavy bleeding, fever, apathy or foul-smelling discharge during the heat.
- Two to eight weeks after the heat: excessive drinking, vomiting, purulent discharge, swollen belly. These can be signs of pyometra, an emergency.
What to remember
Heat: about three weeks, range two to four. Fertile mainly in the second half, even when the bleeding is already fading. First heat at 6 to 12 months, then about every six to seven months, less often in large dogs. Write the dates down: after two or three heats you know your dog's rhythm.
This article does not replace veterinary advice. If your dog shows signs of illness, see your vet.
