Understanding the Heat Cycle of Female Dogs

Updated September 17, 2021
Cute and relaxed dog lying on grass and being petted

Understanding a female's heat cycle can help you prepare for a breeding or prevent an unwanted litter. Find out how the heat cycle works and how to recognize when a female is coming into season.

The Heat Cycle

Dog heat cycles

When a female comes into "heat" or "season," her body is preparing for breeding and the possibility of producing a litter. According to Banfield Pet Hospitals, the cycle is broken into stages.

Fertility Chart

Heat Stage

Length of Time



Nine days

This stage is marked by an increase in a female's estrogen level. She won't be receptive to a male's advances just yet, but she will show many of the signs of heat listed below.


Nine days

During this stage, estrogen levels drop while progesterone levels rise. The female will begin ovulating during this stage, which means a series of eggs will be released from her ovaries and become available for fertilization. She will now begin to be receptive to a male's attempts to breed her. It is during the estrus stage that a dog can become pregnant.


Two months

Progesterone levels are still elevated, but the female will no longer be receptive to a male's attempts to breed with her.


Two to three months

This is the resting stage that lasts until the female comes into heat again.

Age When Heat Commences

While it is not a hard rule, most females come into their first heat cycle around six months of age, although some females wait as long as 12 to 18 months old. Very large breed females may begin cycling as late as 24 months old.

Frequency of Cycles

While many females will hold to a fairly steady schedule of coming into season about every six months, it can vary. Some females will only come into heat once a year, while others may even come into season every four months. However, these "extra" seasons are not always fertile. Once a female has her first season, you can track subsequent cycles to determine what her natural pattern will be.

Calculating the Heat Cycle

It's possible to calculate approximately where a dog is in the heat cycle, though not all dogs will follow the average time periods for each cycle with 100 percent accuracy. A female dog will come into heat twice a year, and younger dogs may not have a regular time interval established until they are about 2 years old. If you know when your dog had her last heat, you can figure out when the next one is coming by counting the days:

  • Proestrus equals about nine days
  • Estrus equals about nine days
  • Diestrus is about two months long, or 60 days in total
  • Anestrus is about two to three months, or between 60 and 90 days total

You can also use an app or online tool such as a dog heat cycle calculator to keep track of your dog's progress.

Signs a Female Is in Heat

Dogs Meeting On Street

Common signs and symptoms you can expect to see when a female is in season include:

  • Mood change - Some females show a change in mood shortly before their season commences, and they may even act a bit touchy. Think of it as the doggie equivalent of PMS.
  • Swollen nipples - Sometimes, but not always, the nipples and breasts will swell slightly. This can also be a sign of a phantom pregnancy, when a female may begin to show signs of being pregnant even if she's not. So, watch if this happens, but it usually resolves itself in a few weeks after the cycle ends.
  • Sudden interest from males - Male studs are great early warning detectors and can smell the change in a female's hormones before she fully comes into heat.
  • Swollen vulva - The vulva can show some swelling, but it is quite variable. Some females hardly swell at all, while others swell up like a golf ball.
  • Tail flagging - When a female is ready to be bred, she'll usually stand quite still while the male investigates her vulva. She'll hold her own tail up and wag it side to side to make sure he catches the scent.
  • Blood discharge - This is usually the surest indicator the heat cycle has begun, with a pinkish, red-colored discharge the first week that usually turns to a tannish color during the fertile period, and then changes back to a reddish color before gradually stopping altogether. Some females keep themselves extremely clean, and it may be difficult to tell if they are in season at all.

How Long Will Bleeding Last?

A female dog will begin to bleed in the initial pro-estrus stage, which can last anywhere from four to 15 days. She may continue to bleed during the next stage, estrus, which will last another four to eight days. A female dog's bleeding will usually begin to lessen in the estrus stage and should stop entirely before diestrus begins.

Caring for Your Female While She's in Heat

Man with dog

It's important to know what to do for your dog while she is in heat. Fortunately, caring for your female while she's in heat is relatively simple.

  • Keep a close eye on her. This is mainly to protect her from an unwanted breeding because males can detect the scent of a female in heat from some distance away, and they'll travel from blocks away to find her.
  • Be extra patient and gentle with her. She may feel a little under the weather during the proestrus stage.
  • While a dog in heat is not in intense pain, they can experience mild pain and discomfort from cramping.
  • Avoid bathing her until she completely stops discharging. That way, you can figure her cervix is closed again, and she'll be less likely to develop a vaginal/uterine infection from the bathwater.
  • If you've determined your female's regular heat cycle pattern and you intend to breed her, have her checked for brucellosis prior to her next heat cycle, and request that the stud dog owner has the male checked, as well. Brucellosis is a bacterial infection that is sexually transmitted between males and females, and it can cause infertility in both sexes.

Always Good to Know

You may never breed your female, but it's still a good idea to have a basic understanding of heat cycles so you know what she's going through. If you want to eliminate all possibility that she'll ever have a litter, you can ask your veterinarian to spay her for you. That way, you'll never have to deal with her heat cycle again.

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Understanding the Heat Cycle of Female Dogs