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Dog Heat Cycle Calculator

Predict your dog's next heat cycle based on breed size and last heat date. Get estimated fertile window and cycle length.

Enter the date your dog's last heat cycle began

Larger dogs tend to have longer cycles between heats

What is a Dog Heat Cycle Calculator?

The Dog Heat Cycle Calculator helps you predict when your dog will go into heat next based on her size and last heat date. Smaller dogs typically cycle every 5–6 months, while giant breeds may only cycle every 9–12 months. Knowing the timing helps with breeding planning, spay scheduling, and managing your dog during heat. This calculator provides estimates — individual dogs may vary. Always consult your veterinarian for medical advice.

Formula

Next Heat=Last Heat Date+Cycle Length (by size)\text{Next Heat} = \text{Last Heat Date} + \text{Cycle Length (by size)}

The cycle length depends on dog size: small dogs (~150 days), medium (~180 days), large (~210 days), and giant breeds (~270 days). The fertile window is typically days 9–14 of the heat cycle.

How to Calculate

  1. 1

    Enter the start date of your dog's last heat cycle in YYYY-MM-DD format.

  2. 2

    Select your dog's size category based on weight.

  3. 3

    Click Calculate to see the predicted next heat date and fertile window.

Worked Examples

Small Dog — Last Heat January 15

Input: Last Heat: 2025-01-15, Size: Small (under 20 lbs)

  1. Cycle length for small dogs: 150 days (~5 months)
  2. Next heat: 2025-01-15 + 150 days = 2025-06-14
  3. Fertile window: days 9–14 of next heat
  4. Fertile: 2025-06-23 to 2025-06-28

Result: Next Heat: 2025-06-14, Fertile Window: Jun 23 – Jun 28, 2025

Giant Breed — Last Heat March 1

Input: Last Heat: 2025-03-01, Size: Giant (90+ lbs)

  1. Cycle length for giant breeds: 270 days (~9 months)
  2. Next heat: 2025-03-01 + 270 days = 2025-11-26
  3. Fertile window: days 9–14 of next heat
  4. Fertile: 2025-12-05 to 2025-12-10

Result: Next Heat: 2025-11-26, Fertile Window: Dec 5 – Dec 10, 2025

Frequently Asked Questions

Most dogs go into heat every 6 months, but it varies by size. Small breeds may cycle every 4–5 months, while giant breeds may only go into heat every 9–12 months. Individual variation is normal.
A typical heat cycle lasts 2–4 weeks. The most fertile period is usually days 9–14, during the estrus phase when the dog is receptive to mating.
Small breeds may have their first heat as early as 4–6 months. Large and giant breeds may not start until 12–24 months. On average, most dogs experience their first heat between 6–12 months of age.
Common signs include swollen vulva, bloody or straw-colored discharge, increased urination, behavioral changes (restlessness, clinginess), and attracting male dogs. Some dogs may also show appetite changes.
Most veterinarians recommend waiting until at least the second or third heat cycle. Breeding too early can lead to complications since the dog may not be physically mature enough for a healthy pregnancy.