Dog in Heat: Signs, Stages and How Long It Lasts

The Four Stages of the Heat Cycle

• Proestrus (about 9 days, range 3 to 21): the vulva swells and there's a bloody discharge. Males are interested, but she won't accept them yet.^2,11
• Estrus (about 9 days, range 3 to 21): she's fertile and will accept a male. The discharge usually lightens to pink or straw-colored, and she may hold her tail to one side ("flagging").^2,6
• Diestrus (about 2 months): the vulva returns to normal and the discharge stops. False pregnancy and pyometra develop in this stage.^2,11,15
• Anestrus (1 to 6 months): a resting phase before the next heat.^11,2

Signs Your Dog Is in Heat

• A swollen vulva, often the very first sign¹
• A bloody discharge that later turns pink or watery^1,6
• Licking her rear end and urinating more often^4,2
• Restlessness, clinginess or irritability, and a smaller appetite^4,2
• Interest from male dogs, which can smell her from a long way off¹

A puppy's first heat is often irregular. Some dogs have a "split heat," where the signs stop and start again a few weeks later, and some small dogs have "silent heats" with hardly any visible signs.^6,2 It can take up to 2 years for cycles to become regular.¹

How to Tell Heat Is Over

Heat is over when her vulva has gone back to its normal size, the discharge has stopped and she's no longer interested in males, or they in her.^2,6 For most dogs this takes 2 to 3 weeks from the first signs.^3,4

Caring for a Dog in Heat

• Keep her away from unneutered males. Walk her on a leash, choose quiet routes and skip dog parks and daycare. Dogs in fenced yards can still find ways to mate.^2,4 Sperm can survive in her body for up to 5 or 6 days, so even an early, brief mating can lead to puppies.¹⁴
• Use dog diapers if you like, but change them every 3 to 4 hours, and remember they don't prevent mating.^4,2
• Keep her busy with puzzle toys and short training games.²
• Watch for illness in the weeks after her heat ends, including thirst, lethargy, vomiting or a discharge.^2,7

Most vets prefer not to spay a dog while she's in heat, because the uterus has a larger blood supply and the surgery can take longer. If your dog is spayed during heat, keep her away from males for 2 to 3 weeks afterward.¹⁶ See spaying dogs, dog pregnancy and swollen vulva in dogs.

Frequently Asked Questions

How long is a dog in heat?

Usually about 2 to 3 weeks in total. She's fertile for about 9 days of that.

How long does a dog bleed in heat?

The bloody stage lasts about 9 days on average. After that the discharge usually turns lighter and more watery.

How often do dogs go into heat?

Usually about twice a year. Small breeds may cycle more often, and giant breeds less often.

At what age does a dog have her first heat?

Usually between 6 and 24 months, earlier in small breeds.

Can a dog get pregnant on her first heat?

Yes. Keep her away from unneutered males from her first heat on.