Dog Heat Cycle Stages: What Each Week Looks Like

If you are living with an unspayed female dog, her heat cycle can feel confusing at first. One week she is clingy, the next she is spotting, and suddenly every male dog in the neighborhood seems very interested. As a veterinary assistant here in Frisco, Texas, I have walked many families through this step by step. The good news is that once you know the stages, you can plan ahead and keep her comfortable and safe.

Quick overview: the 4 stages of a dog heat cycle

A dog heat cycle (estrous cycle) is typically divided into four stages. The timing varies by individual and breed. For many dogs, the visible, “in heat” portion (swelling and discharge) lasts about 2 to 4 weeks. The internal hormone phases continue beyond that.

• Proestrus: early heat. Swelling and spotting are common. Male dogs show interest, but she usually will not accept mating.
• Estrus: fertile window. Discharge often lightens. This is when pregnancy can happen.
• Diestrus: post-ovulation phase that lasts about 60 days. Progesterone stays elevated whether she is pregnant or not. Visible signs often fade partway through this stage.
• Anestrus: resting phase between cycles. This is the lower-hormone “quiet” period before the next heat.

Important: “Week-by-week” is an approximation. Some dogs move faster, some slower, and first heats can be especially unpredictable.

Week 1: Proestrus

What you may see:

• Vulvar swelling is often the first noticeable change.
• Bloody or red-tinged discharge, usually light at first and then increasing.
• More licking of the rear end.
• Behavior changes such as being extra affectionate, restless, or more easily distracted.
• Male dogs show interest, but many females will still move away, sit down, or even snap if a male tries to mount.

What to do this week:

• Assume she could become pregnant soon and start strict supervision now.
• Leash-only outdoors. Even a well-trained dog can bolt when hormones surge.
• Secure your yard. Males can dig, climb, or slip through gaps surprisingly fast.
• Use a well-fitting dog diaper indoors if spotting is messy, but remove it regularly so the area stays clean and dry.

One detail that surprises many families: dog sperm can survive inside the female reproductive tract for several days. That means a mating that happens late in week 1 can still lead to pregnancy once she transitions into her fertile window. So even if she is not “standing” yet, supervision still matters.

Week 2: Estrus

This is the stage most people mean when they say, “She is in heat.” It is also the stage where pregnancy is most likely.

What you may see:

• Discharge often becomes lighter, sometimes watery pink or straw-colored, but it can vary.
• Swelling may soften a bit compared to week 1.
• Flagging behavior: she may move her tail to the side when touched near the back end.
• Standing for males or actively seeking them out.
• Increased urination to spread scent markers.

What to do this week:

• This is the highest-risk time for accidental breeding. Avoid dog parks, daycare, grooming salons, and any off-leash situation.
• Do not rely on diapers as birth control. They are for cleanliness only and can be displaced quickly.
• Keep doors and gates secured. Many accidental pregnancies happen through a brief lapse, like a delivery person opening a gate.

If you do not want a pregnancy, treat weeks 1 and 2 as “no contact with intact males, period.” Sperm can live for days, so early mistakes can still count later.

Week 3: Diestrus

During diestrus, your dog is no longer in her fertile stage, but her body is still influenced by post-ovulation hormones. This stage lasts about two months and is roughly the same length as a canine pregnancy. It is also why some dogs experience a false pregnancy.

What you may see:

• Male interest decreases and she typically stops accepting mounting.
• Discharge tapers off and swelling reduces.
• Possible false pregnancy signs in some dogs: nesting, guarding toys, enlarged mammary glands, or even milk production.
• Mood shifts: some dogs seem more tired or more irritable.

What to do this week:

• Keep her routine steady. Gentle exercise and enrichment can help with restlessness.
• Watch for false pregnancy behaviors. If she is guarding items or seems distressed, contact your veterinarian for guidance.
• Continue supervision outdoors. Fertility is over, but it is smart to keep good habits until all signs have fully resolved.

Week 4: signs fade

By week 4, many dogs look and act more “normal.” The swelling is usually down, and discharge is often gone or minimal.

Here is the key point: this does not mean her cycle is finished on the inside. Most dogs are still in diestrus for weeks after the visible heat signs stop, and progesterone can remain elevated for around 60 days post-ovulation.

What you may see:

• Little to no discharge and minimal swelling.
• Behavior settles back toward baseline, although some dogs still show hormone-related changes.

What to do now:

• Write down the dates. Tracking helps you predict the next cycle and gives your vet useful information.
• Keep an eye out for false pregnancy signs over the next several weeks, especially nesting or mammary enlargement.

Anestrus: the true rest phase

Anestrus is the quiet time between cycles after diestrus ends. Hormones are lower, the reproductive tract returns closer to baseline, and most dogs behave like their normal selves.

Depending on the dog, anestrus often begins roughly 2 to 3 months after the fertile window and can last several months before the next heat.

How often do dogs go into heat?

Most dogs cycle about every 6 months, but the normal range is wide. Some small breeds may cycle a bit more often, and some large breeds cycle less frequently. Young dogs can be irregular at first.

If your dog is going into heat extremely frequently, not at all after maturity, or you notice sudden changes from her normal pattern, it is worth a veterinary check.

Common signs of heat

• Vulvar swelling
• Bloody to pink discharge that changes over time
• Increased licking
• Male dogs lingering, whining, or trying to reach her
• Restlessness, clinginess, or mood changes
• Frequent urination

Safety checklist during heat

Heat management is mostly about prevention and calm routines. Here is what I recommend to most families:

• Leash-only: no off-leash play until the visible heat is fully finished and you are confident she is no longer attracting males.
• Supervise potty breaks: do not leave her alone in the yard.
• Secure fencing: check for gaps, loose boards, and digging spots.
• Limit visitors: if friends have intact males, postpone playdates.
• Crate or separate: if you have an intact male at home, physical barriers matter. A door is better than a baby gate.
• Hygiene: wipe the vulvar area gently if needed, and wash bedding more often.

When to call the vet

Most heats are normal and uneventful, but please reach out to your veterinarian if you notice:

• Heavy bleeding (soaking areas repeatedly) or discharge with a foul odor
• Lethargy, fever, vomiting, or loss of appetite
• Excessive drinking and urinating beyond the typical scent-marking increase
• Swollen belly, painful abdomen, or sudden illness in the weeks after heat, which can be concerning for uterine infection (pyometra)
• Signs of false pregnancy that are intense or causing distress
• A possible accidental mating, especially if it happened during late proestrus or estrus

Trust your instincts. If something feels off, it is always okay to ask.

Spaying timing

Many families ask if they should spay and when. This decision is personal and depends on your dog’s breed, age, lifestyle, and health history. Your veterinarian can help you weigh benefits like pregnancy prevention and reduced risk of certain reproductive diseases against considerations like optimal timing for growth and orthopedic health in some breeds.

If spaying is on your radar, ask your vet about timing based on your dog’s cycle. Many veterinarians prefer to spay during true anestrus (often around 3 to 4 months after a heat) when tissues are less hormonally influenced, which can help minimize surgical bleeding and swelling. Your vet will guide you on the safest timing for your individual dog.

Bottom line

Most heat cycles follow a predictable rhythm: week 1 brings swelling and spotting, week 2 is the fertile window, and then the visible signs often fade by weeks 3 to 4. Internally, though, diestrus continues for about two months before your dog reaches true anestrus. With a little planning and careful supervision, you can keep her safe, comfortable, and stress-free until it passes.