Dogs in heat/coming into season


  • A heat/season is the fertile period of a dog’s cycle when they can get pregnant.
  • Dogs usually have their first heat at around 6 months old, and then every 6-7 months afterwards.
  • Each heat tends to last approximately 16-18 days.
  • Signs of a heat include a swollen vulva (private parts), bleeding, and changes in behaviour.
  • To prevent an unwanted pregnancy, it’s important to keep your dog away from uncastrated males while she’s in season.
  • Once a female dog is speyed, she will stop having seasons and won’t be able to get pregnant.

General information

A heat (or season) is when a female dog is fertile and can become pregnant. During a heat, it’s likely that your dog will behave differently, bleed from her vulva, and become very interested in male dogs.

Most dogs have their first heat when then are about 6 months old, but this varies a lot and can be as late as 2.5 years old. From then on, most dogs have a heat every 6-7 months (approximately twice a year). Most dogs have bigger gaps between their seasons as they get older, but unlike humans (who at some point go through the menopause), dogs continue to come into heat throughout their whole lives unless they are speyed.  Once a dog has been speyed, her seasons stop and she can no longer become pregnant. Being on heat isn’t painful, but can make a dog feel uncomfortable, unsettled and ‘under the weather’. Although some people think that a dog’s bleeding during their season is a dog’s period, it’s actually a sign that they are at their most fertile.​

A dog in season, bleeding from her vulva

A dog in season, bleeding from her vulva

Signs/symptoms and behaviour

Dogs in heat tend to show the following signs:

  • A large, red, swollen vulva
  • Bleeding from the vulva (or a yellow/red/brown discharge)
  • Licking the back end more than usual
  • Weeing more than usual
  • Behaviour changes such as:
    • being over friendly to other dogs
    • roaming to find male dogs
    • mounting and humping
    • standing/moving the tail to one side when touched,
    • becoming anxious and nesting
A small yorkshire terrier in a harness humping another dog outdoors

A female dog in season humping another


What age do dogs have their first heat?

Most dogs have their first heat at around 6 months old, but timings vary a lot between dogs and breeds. Small dogs tend to have their first season earlier than large dogs (some can be as late as 2.5 years old).

How often are dogs in heat?

After their first season, most dogs have a heat every 6-7 months (twice a year). Some dogs have slightly longer or shorter cycles, but they should be regular. Speak to your vet if your dog has irregular seasons. Most dogs have longer gaps between their seasons as they get older (but can still get pregnant).

How long does a dog’s heat/season last for?

Each heat will last for approximately 2-4 weeks, but your dog won’t bleed for the whole time.

How long does a dog in heat bleed?

Dogs in heat tend to bleed for approximately a week to 10 days. Some dogs bleed very heavily and others so lightly that it’s barely noticeable.

Care tips


Your dog will be feeling hormonal, out of sorts and probably a bit confused during her season, so it’s important to keep her happy and distracted. Keep her entertained by playing games and giving her things to do in the house (such as a treat-filled toy), and take her on walks (away from other dogs) to keep her calm.

Preventing pregnancy

During your dog’s heat, she will be very attracted to males and want to mate. To avoid an unwanted pregnancy, you will need to supervise her the whole time she is in season, keep her on a lead and away from other dogs on walks, avoid leaving her alone in the garden, and keep her completely separate from any uncastrated males (including any that live in your household).

Preventing bleeding in the house

Some dogs bleed heavily during their season, and others are much lighter. To keep your house clean you may want to limit your dog’s access to carpeted areas, sofas and bedding, use towels, or consider using a ‘dog nappy’/’dog pants’ to catch the blood.


Does my dog need to have a season before she is speyed?

No, the vast majority of dogs do not need to have a season before they are speyed. However, each dog is different and it’s always a good idea to speak to your vet about the right timing for your dog. 

How much blood is normal for a dog in heat?

As a general rule, big dogs tend to bleed more than small dogs, but it varies a lot, some dogs bleed heavily, some hardly bleed at all, and some are so light that you won’t even notice it. Lots of dogs are also very clean, so you may not see much blood around the house if your dog is grooming themselves a lot. Always contact your vet if you are worried about the amount your dog is bleeding.

Can a dog get pregnant when not in heat?

No, a dog has to be in heat to get pregnant, but it’s important to be aware that not every heat is obvious. If you suspect your dog could be in heat, or it’s roughly the time that she should be, take precautions to stop her getting pregnant or consider neutering her to prevent an unexpected or unwanted litter.

How swollen is too swollen for a dog in heat?

The amount your dog’s vulva swells during their season will be individual to them, but if your dog’s vulva is so swollen that it’s causing them pain or discomfort, contact your vet for advice.

Is a white discharge from female dog in heat normal?

No, a white discharge could be a sign of infection (such as a pyometra) and should always be checked by a vet.

Published: October 2020

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.