🐕 Canine Heat Cycle Calculator
Predict your dog's estrus cycle phases and fertile window
Calculate Your Dog's Heat Cycle
Enter the first day you noticed bleeding or swelling
5 months (Small breeds)
6 months (Average)
7 months
8 months (Large breeds)
9 months
10 months
12 months (Giant breeds)
Smaller breeds cycle more frequently; larger breeds less often
Dogs typically start heat cycles between 6-24 months of age
Small (under 20 lbs)
Medium (20-50 lbs)
Large (50-90 lbs)
Giant (over 90 lbs)
Breed size affects cycle regularity and duration
Most dogs are in heat for 2-4 weeks (average 21 days)
Understanding the Canine Heat Cycle
The canine estrous cycle, commonly known as the "heat cycle," is a critical aspect of female dog reproductive health. Unlike humans, dogs do not menstruate monthly. Instead, they experience estrus cycles typically twice a year, though this varies significantly based on breed size, age, and individual factors.
Understanding your dog's heat cycle is essential for responsible pet ownership, whether you're planning to breed your dog or want to prevent unwanted pregnancies. Our canine heat cycle calculator helps you predict when your dog will enter her next heat cycle and identifies the fertile window when pregnancy is most likely.
The Four Stages of the Canine Heat Cycle
| Phase | Duration | Signs | Fertility |
|---|---|---|---|
| Proestrus | 7-10 days | Bloody discharge, swollen vulva, attracts males but refuses mating | Not fertile |
| Estrus | 5-14 days | Discharge lightens to pink/straw color, actively seeks males, "flagging" tail | FERTILE – Peak breeding time |
| Diestrus | 60-90 days | Discharge stops, no longer receptive, pregnancy or pseudo-pregnancy possible | Not fertile |
| Anestrus | 4-5 months | No signs, reproductive rest period | Not fertile |
How to Use This Canine Heat Cycle Calculator
To get accurate predictions from our calculator, you'll need to provide:
- Last Heat Start Date: The first day you noticed bleeding or vulvar swelling during your dog's most recent heat cycle.
- Average Cycle Length: Most dogs cycle every 6 months, but small breeds may cycle every 5 months while giant breeds may only cycle once yearly.
- Your Dog's Age: Younger dogs may have irregular cycles that stabilize with age.
- Breed Size: This helps us adjust predictions based on typical breed patterns.
- Heat Duration: How long your dog's heat typically lasts (usually 2-4 weeks).
💡 Pro Tip: Keep a calendar or journal of your dog's heat cycles. After 2-3 cycles, you'll have much more accurate data for predictions, as individual dogs can vary significantly from averages.
Signs Your Dog is Going Into Heat
Recognizing the early signs of heat can help you prepare and manage your dog appropriately:
- Swollen vulva: Often the first noticeable sign, occurring 1-2 days before bleeding
- Bloody vaginal discharge: Ranges from light spotting to heavier flow
- Increased urination: Dogs urinate more frequently to spread pheromones
- Behavioral changes: May become more affectionate, anxious, or restless
- Tail flagging: Holding tail to the side when touched near the hindquarters
- Attracting male dogs: Intact males may appear at your property
- Licking genital area: More frequent grooming of the vulvar region
Breed Size and Heat Cycle Frequency
Your dog's breed size significantly impacts her heat cycle patterns:
- Small breeds (Chihuahua, Yorkie, Pomeranian): May cycle 3-4 times per year, often starting heat as early as 4-6 months of age
- Medium breeds (Beagle, Cocker Spaniel, Bulldog): Typically cycle twice yearly, starting around 6-12 months
- Large breeds (Labrador, German Shepherd, Golden Retriever): Usually cycle every 6-8 months, first heat at 9-12 months
- Giant breeds (Great Dane, Mastiff, Saint Bernard): May only cycle once per year, with first heat possibly delayed until 18-24 months
Managing Your Dog During Heat
When your dog is in heat, consider these management strategies:
- Containment: Keep your dog securely indoors or in a fully fenced yard. Male dogs can detect females in heat from miles away and may attempt to reach her.
- Supervision: Never leave your dog unattended outside during heat, even briefly.
- Leash walks only: Avoid off-leash areas during the entire heat cycle.
- Doggie diapers: Use canine sanitary products to manage discharge and protect your home.
- Extra attention: Your dog may need additional comfort and reassurance during this time.
- Separate from intact males: If you have unneutered male dogs, keep them completely separated.
When to Consult a Veterinarian
While heat cycles are normal, certain situations warrant veterinary attention:
- First heat before 4 months of age or no heat by 24 months
- Cycles occurring more frequently than every 4 months
- Heat lasting more than 4 weeks
- Foul-smelling or unusual colored discharge
- Excessive lethargy, vomiting, or loss of appetite during heat
- Signs of pyometra (uterine infection): increased thirst, abdominal swelling, or pus-like discharge
Spaying Considerations
If you don't plan to breed your dog, spaying offers numerous health benefits including eliminating heat cycles, preventing pyometra, and reducing the risk of mammary tumors. Discuss the optimal timing for spaying with your veterinarian, as recommendations vary based on breed, size, and individual health factors.
⚠️ Important: This calculator provides estimates based on average data. Individual dogs vary significantly. Always consult with your veterinarian for breeding decisions or if you notice any abnormalities in your dog's reproductive cycle.
🐕 Heat Cycle Predictions
';
resultHTML += 'Current Cycle Phase:' + currentPhase + '
';
resultHTML += 'Days Until Next Heat:' + daysUntilHeat + ' days
';
resultHTML += 'Next Heat Start (Est.):' + formatDate(nextHeatStart) + '
';
resultHTML += 'Next Heat End (Est.):' + formatDate(heatEndDate) + '
';
resultHTML += 'Proestrus Phase:' + formatDate(proestrusStart) + ' – ' + formatDate(proestrusEnd) + '
';
resultHTML += 'Estrus (Fertile) Phase:' + formatDate(estrusStart) + ' – ' + formatDate(estrusEnd) + '
';
resultHTML += 'Peak Fertility Window:' + formatDate(fertileWindowStart) + ' – ' + formatDate(fertileWindowEnd) + '
';
resultHTML += 'Following Heat (Est.):' + formatDate(followingHeat) + '
';
resultHTML += 'Adjusted Cycle Length:' + adjustedCycleLength + ' days (~' + (adjustedCycleLength / 30).toFixed(1) + ' months)
';
resultHTML += '🔔 Reminder: Keep your dog secured and supervised starting around ' + formatDate(new Date(nextHeatStart.getTime() – 7 * 24 * 60 * 60 * 1000)) + ' (one week before predicted heat). Male dogs can detect females in heat from great distances.
';
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = resultHTML;
resultDiv.style.display = "block";
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'start' });
}
function formatDate(date) {
var options = { weekday: 'short', year: 'numeric', month: 'short', day: 'numeric' };
return date.toLocaleDateString('en-US', options);
}
var today = new Date();
var threeMonthsAgo = new Date();
threeMonthsAgo.setMonth(threeMonthsAgo.getMonth() – 3);
document.getElementById("lastHeatDate").value = threeMonthsAgo.toISOString().split('T')[0];