Dogs
How Long Are Dogs in Heat? The Complete Heat Cycle Explained
Published 2026-05-01 • 10 min read
A dog's heat cycle — called estrus — typically lasts 2 to 4 weeks. But "in heat" is more nuanced than a single on/off state. There are four distinct stages. The fertile window is shorter than most owners realize. And the behaviors and physical changes at each stage vary significantly. Here's everything you need to know.
Educational guide only. This article does not replace a veterinary exam, diagnosis, or emergency care.
Stage 1 — Proestrus (7–10 Days)
The beginning of the cycle. The vulva swells noticeably. Bloody vaginal discharge appears — ranging from bright red to light pink.
The dog is not yet fertile. She attracts males but will actively reject mounting attempts. Behavioral changes: clinginess, restlessness, more frequent urination (to spread scent).
Duration: 7–10 days on average. Can range from 3–17 days.
Stage 2 — Estrus (5–9 Days)
This is the fertile window. The discharge lightens in color — straw-colored, pinkish, or nearly clear.
The female becomes receptive to males. She may "flag" — holding the tail to the side when touched near the base. This is a clear sign she is ready to mate.
Ovulation typically occurs 2–3 days into estrus. Eggs remain viable for 2–5 days after ovulation.
This is the window in which pregnancy can occur.
Stage 3 — Diestrus (60–90 Days)
The post-fertile phase. The dog is no longer receptive to males. Discharge decreases and stops.
If the dog is pregnant, diestrus lasts through the approximately 63-day gestation period.
If the dog is not pregnant, the body still goes through hormonal changes similar to pregnancy. This is called false pregnancy (pseudopregnancy) and can cause nesting behavior, mammary gland development, and even milk production.
Stage 4 — Anestrus (4–5 Months)
The resting phase. Hormonal inactivity. No signs of heat. The body prepares for the next cycle.
In most dogs, the full cycle from one heat to the next is approximately 6 months (two cycles per year). Some breeds cycle only once a year, particularly Nordic breeds like the Basenji and Tibetan Mastiff.
How Long Is a Dog "In Heat" Total?
The heat cycle (proestrus + estrus combined) typically lasts 2–4 weeks.
The fertile window (estrus only) is 5–9 days within that period.
Most owners notice the onset of heat (bleeding, swelling) and assume the fertile window is immediate. It's not — the dog becomes receptive and fertile only in stage 2, after the first week of proestrus.
When Does a Dog First Go Into Heat?
Most dogs have their first heat between 6 and 24 months of age.
Small breeds typically start earlier — as young as 6 months.
Large and giant breeds may not have their first heat until 18–24 months.
The first heat is often irregular and may be shorter or lighter than subsequent cycles.
Signs a Dog Is in Heat
Some female dogs are fastidious groomers and clean the discharge — making it easy for owners to miss the early stages.
Checklist
- Swollen vulva — often the first visible sign
- Bloody vaginal discharge — color ranges from red to pink to straw
- Increased urination — instinctive scent marking
- Behavioral changes — clingier, anxious, or restless
- Excessive licking of the genital area
- Flagging — tail raised or held to the side when approached
- Increased attention from intact male dogs
Managing a Dog in Heat
Prevent Unwanted Pregnancy
An intact male dog can detect a female in heat from extraordinary distances. During the fertile window (estrus), do not leave your dog unattended outdoors even for minutes.
Walk on a leash at all times. Avoid dog parks.
Males will breach fences and gates to reach a female in estrus. Treat containment as if it's a potential emergency.
Hygiene
Dog heat diapers (also called dog pants) absorb discharge and protect furniture. Change regularly to prevent skin irritation.
Avoid full baths during heat — bathing can introduce bacteria. Use warm cloths to clean the vulval area.
Behavioral Management
Increased rest, shorter walks during peak discharge days, consistent routine, and calm management help dogs through the hormonal changes.
Some dogs become anxious or attention-seeking. Extra affection and predictable routine helps.
Spaying — The Permanent Solution
Spaying (ovariohysterectomy) ends the heat cycle permanently.
Vets recommend spaying before the first heat in many cases — it dramatically reduces the risk of mammary tumors and eliminates the risk of pyometra (a life-threatening uterine infection).
Optimal spay timing varies by breed size. Discuss timing with your vet — there are nuances, particularly for large and giant breeds where early spaying may affect musculoskeletal development.
❓ Frequently Asked Questions
Frequently Asked Questions
The full heat period (proestrus + estrus) typically lasts 2–4 weeks. The fertile window is shorter — approximately 5–9 days during the estrus stage, usually in the second week.
Most dogs cycle twice per year — approximately every 6 months. Small breeds may cycle 3 times per year. Large and giant breeds often cycle only once per year. Basenjis are notable for a single annual cycle.
Heat is ending when the vulva returns to normal size, discharge stops, and the dog no longer flags or shows interest in males. This typically happens by day 18–25 of the cycle.
Yes — a dog is biologically capable of getting pregnant in her first heat. However, breeding at the first heat is generally not recommended. The body is still maturing, particularly in larger breeds.
A silent heat occurs when the dog goes through the hormonal changes of estrus with minimal external signs — little to no discharge or vulvar swelling. The dog is still fertile. Common in young dogs during their first cycles.
Dogs may experience discomfort during heat — cramping similar to menstruation has been suggested, though it's difficult to assess in animals. Behavioral changes like restlessness and clinginess likely reflect this discomfort. Most dogs manage without any intervention.