How old is a dog when they go into heat?

Dogs go in heat twice a year as soon as they reach their sexual maturity. But when is it? When we first meet a dog owner with a new female puppy in our veterinary clinic, one of our first conversations is about breeding and spaying. We strongly believe that spay surgery not only helps prevent diseases such as mammary cancer and uterine infections but also reduces the stress of having a female dog that goes into heat with the possibility of an unwanted pregnancy. This is even more critical if they have male dogs in the household as well. We know from experience as our first male dog, a Labrador Retriever wasn’t neutered.  He was more than a handful with his hormone filled antics.  Having a female in heat near him would have been intolerable. 

In this article, you’ll learn how old a dog is when they go into heat for the first time, how often she’ll have her dog heat cycle, and should you worry if her heat cycle appears to be late.

Table of Contents

• At what age do dogs go into heat?
• How many times a year is a dog in heat?
• How long can a dog go without going into heat?
• Can my dog have too many heats?
• What if my dog hasn’t come into heat by age 2?
• Why is my dog not coming into heat?

At what age do dogs go into heat?

6 months. Female dogs usually has her first heat cycle or estrus cycle when she’s reached her sexual maturity. In most cases, it is between six and twelve months of age. However, exceptions are possible. And not always they should be considered abnormalities. Smaller dog breeds tend to come in heat at younger ages as they mature earlier, both sexually and physically.

How many times a year is a dog in heat?

2 times per year.  On average,  female dogs will have 2 heat cycles per year. This is breed dependent however. A giant or large breed dog may only have one heat cycle every 12 months which we’ve seen. We’ve also seen small dogs and toy breeds go through their dog heat cycle three times a year.  

The most common cycling frequency for female dogs is every five to nine months. Besides, the cycling is independent on seasonal variation, unlike it is for cats, for example that have heat cycles which are influenced by the sun.

There is no such thing as “spring madness” for dogs because they cycle on a pattern independent of each other. You may have heard that female dogs in the same household can synchronize their heat cycles. However, there’s no evidence this happens and most likely this is just a myth.

For example, some dogs, by default, go in heat once a year. For instance, Basenji dog breed goes in heat only once a year even though they are considered a medium sized breed. Younger dogs can go in heat less frequently.

Often, quite the contrary occurs, and many dogs go in heat more often than twice a year. Three times a year is quite common and is considered normal.

How long can a dog go without going into heat?

2 years. A female puppy should have her first estrus cycle by the age of 2.  Even a giant Great Dane should have her first cycle by that age.  As your dog ages, she’ll cycle less frequently.  She can however still become pregnant.  And no, dog diapers won’t prevent an unwanted pregnancy.  They are however great to contain the bloody discharge.

Can my dog have too many heats?

Some dogs go into heat four times a year. The latter is already excessive and you may face several problems if you intend to breed your dog. For example, not all of these heats allow your dog to become pregnant. The dog shows the signs of the heat, but their body can’t carry on with the implantation. Most likely, it’s because your dog’s body did not have enough time to recover from the previous heat.

Also, there are several more abnormalities, like split heat, when the female dog starts her heat cycle, but suddenly stops, and begins in several weeks again. This may lead to the impression that the dog goes in heat every month.

One more thing to know is that sometimes heat can go by without any apparent symptoms. It is called a silent heat, and, if between two regular heats is one silent, the owner may observe that the dog goes in heat less often than expected

What would cause a dog to never go into heat?

Illness or poor health such as malnutrition. Most veterinarians (me included) suggest not to worry about a dog not going into her heat until she has reached two years of age. This is especially true in larger dog breeds such as a Great Dane. In our vet clinic, we see some giant breeds have their first heat cycle between 12 and 18 months of age.  Large breeds a German Shepard we see in the 9 to 12 months of age for their first heat.  Small or toy breeds we see tend to happen around the 6 month of age mark. But for the most part, we see that most dogs go into their dog heat cycle within the first year.  It’s not uncommon to have some delays and that isn’t a serious issue. The reason for this is the variation of when a female dog reaches puberty. In an article from Canine Medicine, it’s noted that female dogs reach puberty between 6 and 14 months of age.

However, if your dog is already past two years of age and hasn’t yet come into heat, please consult your veterinarian. The reasons for this happening may vary from harmless to dangerous.

Why is my dog not coming into heat?

Genital disease and poor general health. These are the two most common causes for a dog not coming into heat with a dog being in poor general health the most common one we’ve seen. There are less common other reasons why your dog might not be coming into heat, again we encourage you to consult with your veterinarian.

You should also know about a silent heat, which is heat without apparent symptoms. Even though silent heat is quite common in young dogs and smaller dog breeds, it is considered abnormality which may make you assume, a dog has not had her first heat heat yet. You can learn more about this and other abnormalities in our article Abnormal heat cycles in female dogs.

However, it’s possible the symptoms of your dog being in heat weren’t strong enough to notice. For example, your female dog may be very clean and she licks up any vaginal discharge before you notice it or her doing so. Also, it is possible that you the dog owner may have recognized the different and subtle symptoms she was showing for something else.  If you aren’t sure, please consult with your veterinarian.

In any case, it’s quite common for dogs not to come have their first heat cycle until two years of age. Especially if you have a larger breed female dog. If you are worried about your dog’s health, please consult with your veterinarian.

You have learned how old a dog is when they go into heat for the first time, how often she’ll have her dog heat cycle, and should you worry if her heat cycle appears to be late. This will go a long way towards a healthy and happy life with your pet dog. And keeping your Pet Happy is what we all want.

This article is a part of our Dog Heat Cycle: A Comprehensive Guide for Pet Owners.

Next: How often do dogs go in heat
Previous: Why do dogs go in heat?