Understanding Your Dog's Heat Cycle: Signs, Stages & Timing

For owners of intact (unneutered) female dogs, understanding the heat cycle is essential — whether you are considering responsible breeding or simply want to know what to expect and how to manage this period. This guide explains each stage of the canine reproductive cycle in plain language.

What Is a Heat Cycle?

A "heat cycle" — formally called the oestrous cycle — is the recurring reproductive cycle of intact female dogs. Unlike humans, dogs do not menstruate monthly. Most female dogs cycle approximately twice per year, with intervals typically ranging from 5 to 8 months depending on breed and individual variation.

Giant breeds like Great Danes and Saint Bernards may only cycle once per year, while smaller breeds can sometimes cycle more frequently.

The Four Stages of the Canine Heat Cycle

Stage 1: Proestrus (Average: 9 days, range 3–17 days)

Proestrus is the beginning of the heat cycle and the stage most owners first notice. Signs include:

• •Swelling of the vulva — often the first visible sign
• •Bloody vaginal discharge — ranges from bright red to pink or straw-coloured
• •Increased attention from male dogs, though the female will typically refuse mounting at this stage
• •Changes in behaviour — some dogs become more affectionate, others more restless or irritable
• •Frequent urination — scent-marking behaviour to signal reproductive status

During proestrus, the female is not yet receptive to mating. Progesterone levels are low and oestrogen is rising.

Stage 2: Oestrus — The Fertile Window (Average: 9 days, range 5–13 days)

Oestrus is the stage when the female is receptive to mating and ovulation occurs. Signs that oestrus has begun include:

• •Change in discharge — typically lightens from red to a straw or pinkish colour
• •Receptive behaviour — the female may stand still and deflect her tail to the side (called "flagging") when approached by a male
• •Soft, slightly less swollen vulva compared to proestrus

Ovulation typically occurs around days 10–14 from the first day of proestrus, though this varies. Canine eggs remain viable for 48–72 hours after ovulation, and sperm can survive in the reproductive tract for several days, giving a fertile window of approximately 5–7 days around ovulation.

Stage 3: Dioestrus (Average: 60–90 days)

Whether or not the dog has mated and become pregnant, dioestrus follows oestrus and is characterised by elevated progesterone levels. In pregnant dogs, this stage covers the gestation period (approximately 63 days from fertilisation). In non-pregnant dogs, progesterone still remains elevated for several weeks before declining.

During dioestrus, some intact non-pregnant dogs experience pseudopregnancy (phantom pregnancy) — a hormonally driven condition where the dog shows signs of pregnancy including nesting behaviour, milk production, and mothering of objects. This is a normal hormonal response in dogs and typically resolves on its own, though severe cases benefit from veterinary attention.

Stage 4: Anoestrus (Average: 4–5 months)

Anoestrus is the reproductive resting phase between cycles. The reproductive tract is hormonally quiet, there are no visible external signs, and the dog is not receptive to mating. This phase is entirely normal and necessary for reproductive tract restoration before the next cycle begins.

How to Track Your Dog's Cycle

Keeping a simple record of each heat cycle helps you:

• •Predict when the next cycle will occur
• •Identify when the fertile window is approaching
• •Detect any changes in cycle length or character that might warrant a vet visit

Note the date the first signs appeared, the character and duration of discharge, and any changes in behaviour. Most cycles follow a fairly consistent personal pattern once established.

Managing a Dog in Heat

If you are not planning to breed your dog, the heat period requires careful management:

• •Keep intact females securely away from intact males during oestrus (male dogs can detect a female in oestrus from considerable distances)
• •Use washable dog pants or nappies indoors to manage discharge
• •Keep outdoor time supervised and on a lead
• •Be aware that males may be persistent — accidental matings can occur quickly

When to Consult a Vet

Contact your vet if:

• •Your dog's first heat has not occurred by 24 months of age
• •Cycles are very irregular, very prolonged, or have changed significantly
• •There is an unusually large amount of discharge or the discharge has a strong odour
• •Your dog shows signs of a phantom pregnancy that are causing distress
• •You are considering spaying (neutering) and want to discuss the optimal timing

Use Our Dog Heat Cycle Calculator

Track your dog's heat cycle and calculate the approximate fertile window with our interactive tool.