PROESTRUS
Jul 4, 2026 - Jul 13, 2026
Bloody discharge begins; males are attracted but the female is usually not receptive.
4-stage cycle timeline
Dog Heat Cycle Calculator
Know when the next heat may start, when she is fertile, and what to expect at each stage whether you are planning a litter or preventing one.
4-stage timeline
Breeding window
Breed-adjusted prediction
I want to
Next heat expected
Dec 17, 2026 - Jan 14, 2027
Most likely around Dec 31, 2026 based on breed or size average.
Next heat in
180 days
Cycle result
Heat cycle timeline for your dog
Current stage: Proestrus, day 1 of about 9
ESTRUS
Jul 13, 2026 - Jul 20, 2026
The fertile stage; discharge lightens and the female may stand for males.
DIESTRUS
Jul 20, 2026 - Oct 3, 2026
Post-heat stage; progesterone stays elevated whether or not pregnancy occurred.
ANESTRUS
Oct 3, 2026 - Dec 31, 2026
Reproductive rest period with low hormone activity and no heat signs.
Proestrus
Bloody discharge begins; males are attracted but the female is usually not receptive.
- Vulva swelling
- Bloody discharge
- Frequent licking
- Male dogs show interest
Start isolation from intact males and begin daily observation.
Estrus
The fertile stage; discharge lightens and the female may stand for males.
- Discharge turns pink or straw colored
- Flagging behavior
- Receptive to males
- Highest pregnancy risk
Use strict prevention or schedule veterinary-timed breeding.
Diestrus
Post-heat stage; progesterone stays elevated whether or not pregnancy occurred.
- Discharge stops
- No longer receptive
- Possible false pregnancy signs
- Pregnancy confirmation window if bred
Watch for false pregnancy or schedule pregnancy confirmation if mating occurred.
Anestrus
Reproductive rest period with low hormone activity and no heat signs.
- No discharge
- No receptivity
- Hormonal rest
- Often best spay timing
Plan routine care, prevention, or spay discussion during this quieter stage.
Mode-specific guide
Pregnancy prevention guide
Danger period: Jul 4, 2026 - Jul 22, 2026. Keep her away from intact males through this date, including the two-day buffer after estrus.
- Use a leash outdoors at all times.
- Avoid dog parks and off-leash areas.
- Separate from intact males at home.
- Consider spaying during anestrus: Oct 3, 2026 - Dec 31, 2026.
Cycle history tracker
Your dog's cycle history
Save at least two cycle start dates to calculate an average interval.
Complete guide
The 4 stages of the dog heat cycle
Your dog just started her heat cycle, or maybe you are trying to plan the perfect breeding window. Either way, the useful answer is not just one date. It is a staged timeline that explains what is happening and what owners should do next.
Stage 1
Proestrus
Proestrus is the visible beginning of heat and averages about 9 days. Estrogen rises while progesterone remains low. Owners usually notice vulva swelling, bloody discharge, frequent licking, and increased interest from male dogs. The female may flirt, but she usually refuses mating by sitting, turning away, or guarding her rear. This is the stage when many first-time owners mistake normal discharge for injury. Start leash-only management, keep her away from intact males, and use hygiene pants only as a cleanliness tool, not as pregnancy prevention.
Stage 2
Estrus
Estrus is the fertile stage and averages about 7 days. Estrogen falls, progesterone begins rising, and the LH surge triggers ovulation. Discharge often becomes lighter pink or straw colored, the vulva softens, and the female may flag her tail to one side and stand for males. Ovulation often occurs about 2 days after the LH surge, but canine eggs need another 2 to 3 days to mature. Breeders should confirm timing with progesterone testing when possible. Prevention-focused owners should use their strictest separation during this stage.
Stage 3
Diestrus
Diestrus follows estrus and often lasts 60 to 90 days. The female is no longer receptive, discharge stops, and the vulva returns toward normal size. Progesterone stays high whether or not pregnancy occurred, which is why non-pregnant dogs can show false pregnancy signs such as nesting, mammary development, clinginess, or even milk production. If mating occurred, this is the pregnancy confirmation window; many clinics use ultrasound around days 25 to 28 after breeding. If she was not bred, watch for false pregnancy or unusual discharge.
Stage 4
Anestrus
Anestrus is the reproductive rest period and commonly lasts 4 to 5 months, although it can be shorter in small breeds and much longer in giant or seasonal breeds. Hormone activity is low, there is no discharge, and the female is not fertile. This quiet window is often the preferred time to discuss spay surgery because the uterus is smaller and less blood-filled than during heat. It is also the best time to review body condition, nutrition, vaccination status, and whether future breeding is appropriate.
Cycle frequency
How often do dogs go into heat?
Most intact female dogs cycle once or twice per year, but size and breed can change the rhythm. Small dogs may return to heat every 4 to 6 months, while giant breeds may cycle only once a year. Basenjis and Tibetan Mastiffs are notable seasonal examples.
First heats are less reliable for prediction. The first 1 to 2 heat cycles are often irregular, and most dogs establish a clearer pattern after the second or third cycle. Female dogs do not have menopause, but older dogs may cycle less predictably and carry higher pregnancy risk.
SizeFrequencyIntervalFirst heat
Toy / small dogs
2-3 times per year
Every 4-6 months
6-9 months
Medium dogs
About twice per year
About 6 months
8-12 months
Large dogs
1-2 times per year
Every 6-8 months
12-18 months
Giant dogs
About once per year
About 12 months
18-24 months
Signs of heat
Signs your dog is in heat
Heat signs combine physical changes and behavior changes. The flag test can help identify estrus: gently touch near the base of the tail, and a receptive female may move her tail to the side and stand still. Use this as a clue, not a medical test.
Physical signs
- Swollen vulva, often the earliest visible signal
- Bloody discharge that later becomes pink or straw colored
- Frequent licking of the vulva
- More frequent urination to spread scent signals
Behavior changes
- Restlessness, clinginess, or mild appetite changes
- Trying to escape or seek male dogs
- Interest in males during proestrus but refusal to mate
- Flagging and standing still during estrus
Do not confuse with
- UTI, which may cause odor, pain, or abnormal urination
- Pyometra, especially foul discharge with illness
- False pregnancy signs during diestrus
- Any severe lethargy, fever, or foul smell
Breeding timing
How to maximize conception timing
Timing matters because canine eggs are not ready immediately at ovulation. They need about 2 to 3 days to mature, while sperm can survive several days in the reproductive tract. The practical breeding window often falls after estrus begins, but visual cues alone can miss the true ovulation date.
After a confirmed mating, use the Dog Pregnancy Calculator to manage pregnancy after breeding, estimate the due window, and plan confirmation checks.
Least precise
Observation
Lighter discharge and flagging suggest estrus, but behavior alone can be off by several days. It is useful for broad planning, not precision breeding.
Often within 1-2 days
Vaginal cytology
A veterinarian checks cell changes under a microscope. High cornification supports estrus-stage timing and can guide when to begin progesterone testing.
Most practical precision
Progesterone testing
Blood progesterone helps identify ovulation. Many breeders test every 2 days starting around day 5 to 7 of proestrus until timing is clear.
Spay timing
Should you spay your dog? Heat-cycle timing matters.
The calculator identifies anestrus because it is often the quieter surgical-planning window. This does not replace your veterinarian's advice; the right timing depends on breed, size, age, health, and risk tolerance.
Anestrus is often the preferred spay window because reproductive tissues are quieter.
Spaying eliminates pyometra risk and prevents accidental pregnancy.
Early spay timing should be discussed carefully in large and giant breeds because orthopedic tradeoffs may matter.
After spay, calorie needs may fall, so feeding plans often need adjustment.
FAQ
Dog heat cycle FAQ
How long does a dog stay in heat?
Most dogs are visibly in heat for about 2 to 3 weeks when proestrus and estrus are counted together. Proestrus often lasts around 7 to 10 days and includes swelling and bloody discharge. Estrus often lasts about 5 to 9 days and is the main fertile window. The exact length varies by dog, breed size, age, and whether the cycle is one of the first few heats.
How often do dogs go into heat?
Many medium dogs cycle about twice per year, but size matters. Small dogs may cycle 2 to 3 times per year, large dogs may cycle every 6 to 8 months, and giant breeds may cycle about once yearly. Basenjis, Tibetan Mastiffs, and some wolf-like breeds can show seasonal patterns. The first 1 to 2 cycles are often irregular.
When is the best time to breed a dog?
The best practical breeding window is usually around days 2 to 5 of estrus, but the most accurate answer comes from progesterone testing. Canine eggs need time to mature after ovulation, and sperm can survive several days inside the reproductive tract. That is why planned breedings often use progesterone testing and every-other-day breeding rather than one visual guess.
How do I know when my dog's heat is over?
Heat is usually ending when discharge stops, vulva swelling reduces, and the female rejects male attention again. For pregnancy prevention, add a buffer rather than assuming the first quiet day is safe. The calculator uses proestrus plus estrus plus a two-day buffer as the danger period because timing can vary.
Can a dog get pregnant during her first heat?
Yes. A dog can become pregnant during her first heat, but breeding at the first heat is usually not recommended. Young dogs may still be physically immature, early cycles can be irregular, and pregnancy can carry higher risk. Discuss breeding age, health testing, and breed-specific risks with a veterinarian before any planned litter.
How long after heat can a dog be spayed?
Many veterinarians prefer waiting until anestrus, often at least a few months after heat, because the uterus and blood vessels are less active. Exact timing depends on the dog, the clinic, and medical urgency. Avoid treating this calculator's spay window as surgical clearance; it is a planning prompt for a vet discussion.
What are the signs that a dog is going into heat?
The earliest common signs are vulva swelling, bloody discharge, increased licking, and more frequent urination. Behavior may also change: some dogs become clingier, restless, more interested in scent marking, or more determined to escape. During estrus, flagging and standing for males suggest receptivity.
Can dogs go into heat while nursing?
It is uncommon for most dogs to cycle during active lactation, but reproductive timing can vary. A nursing dog with discharge, fever, pain, poor appetite, or illness should be examined rather than assumed to be in a normal heat. Postpartum discharge and uterine infection can be confused by owners.
How do I stop my dog from going into heat?
Spaying is the permanent way to prevent heat cycles. Hormonal suppression methods exist in some settings, but they can carry health risks and are not casual owner tools. If heat management is difficult, talk with your veterinarian about timing a spay during an appropriate cycle stage.
My dog's heat cycles are irregular. Is that normal?
Irregular timing is common during the first 1 to 2 cycles and in some seasonal or giant breeds. Persistent irregularity in an adult dog can deserve veterinary evaluation, especially if cycles are very frequent, absent, prolonged, or paired with illness. Thyroid disease, ovarian cysts, and uterine disease are examples of issues a vet may consider.
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References
Source context
- Concannon PW. Reproductive cycles of the domestic bitch. Animal Reproduction Science. 2011.
- Society for Theriogenology. Canine breeding management and reproductive timing guidance.
- Merck Veterinary Manual. Reproductive cycles and breeding management in dogs.
- American College of Theriogenologists. Owner education resources on canine reproduction.