Dog Health
Dog in Heat
Published Last updated 2 min read
Quick answer
A dog "in heat" is in the fertile phase of her reproductive cycle. Most unspayed dogs come into heat about twice a year, starting between 6 and 12 months of age (later in large breeds). A heat lasts 2–4 weeks, with telltale signs including a swollen vulva, bloody discharge, and increased attention from male dogs.
Key takeaways
- Usually 6–12 months. Large and giant breeds may not start until 18–24 months of age.
- Yes — though many vets advise against breeding during the first heat cycle.
- Many vets recommend waiting a few weeks after the heat ends. Ask your vet for the best timing for your dog.
Help street dogs abroad with WARN: sponsor a dog or donate · Karachi street-dog appeal
What does "in heat" mean?
Heat (estrus) is part of the estrous cycle — the recurring period when an intact (unspayed) female dog is fertile and can become pregnant. Spaying removes the ovaries and uterus, so spayed dogs do not go into heat.
What are the 4 stages of the dog heat cycle?
| Stage | Typical length | What happens |
|---|---|---|
| Proestrus | ~9 days | Swollen vulva, bloody discharge; attracts males but will not mate |
| Estrus | ~9 days (range 3–21) | The fertile window; discharge lightens; she becomes receptive to males |
| Diestrus | ~2 months | Cycle winds down; pregnant or not, hormones shift |
| Anestrus | ~4 months | Resting phase until the next cycle |
What are the signs a dog is in heat?
Common signs include a swollen vulva, blood-tinged to straw-coloured discharge, more frequent urination (scent-marking), restlessness or clinginess, "flagging" (moving the tail to one side), and strong interest from male dogs. Some dogs keep themselves very clean, so discharge is not always obvious.
How long does a dog stay in heat?
The visible heat usually runs 2 to 4 weeks. Cycle frequency varies by size: small breeds may cycle every 4–6 months, while some large and giant breeds cycle only once a year.
How do I care for a dog in heat?
Keep her securely away from intact males at all times — dogs can mate through fences and escape even determined barriers. Walk her on a lead, supervise the garden, and consider a washable doggy nappy for discharge. Provide extra comfort and patience with behaviour changes.
If you do not plan to breed her, ask your vet about spaying, which also lowers the risk of mammary tumors and pyometra — a life-threatening uterine infection.
Sources & further reading
Facts in this guide are rewritten in plain English from publicly available UK advice. We name the organisation where a specific point comes from their guidance. Links below go to the original pages — use them to read the source material directly.
PETHEALTH+ is independent. These organisations do not sponsor, approve, or partner with this website. Guidance checked against sources listed below (last updated 2026-06-08).
- Dog Pooping Blood
- Hot Spots on Dogs
- Adder Snake Bites in Dogs UK
- Adopting a Rescue Dog in the UK
- Alabama Rot in Dogs UK
- Bloat in Dogs (GDV)
- Can Dogs Eat Apples UK?
- Can Dogs Eat Avocado UK?
Also see symptoms, symptom checker, and poison guide.
Frequently Asked Questions
- At what age does a dog first go into heat?
- Usually 6–12 months. Large and giant breeds may not start until 18–24 months of age.
- Can a dog get pregnant on her first heat?
- Yes — though many vets advise against breeding during the first heat cycle.
- When can I spay my dog after a heat?
- Many vets recommend waiting a few weeks after the heat ends. Ask your vet for the best timing for your dog.