Predict your female dog's next heat cycle and fertile period. Track estrous cycles for breeding planning or spay scheduling.
Last updated: March 2026
A dog heat cycle, also called estrous or season, is the reproductive cycle in female dogs when they become fertile and can conceive. Dogs typically experience heat cycles every 6-8 months (twice per year), though this varies substantially between individuals. Cycle length depends on breed size, genetics, health status, and age. First cycles may be irregular or shorter/longer than subsequent ones.
The canine estrous cycle consists of four stages: proestrus (average 9 days), estrus (average 9 days), diestrus (60-90 days), and anestrus (4-5 months). Proestrus is marked by vulvar swelling and bloody discharge but females aren't yet receptive to males. Estrus is the fertile period when ovulation occurs and females accept male attention. The entire "heat" most owners notice lasts about 18-21 days covering proestrus and estrus combined.
Important variation: Individual dogs have highly variable cycles. Some dogs maintain reliable 6-month intervals; others are irregular and unpredictable. Breeding females especially need to be monitored with veterinary guidance and (ideally) hormone testing or cytology to pinpoint ovulation, not just date-based assumptions. For contraception planning, assume the cycle could come early or late. This calculator provides a planning estimate only—not a reliable prediction for any specific dog.
Predict heat cycles using previous cycle dates:
Let's predict the next heat for a dog whose last cycle started March 1, 2026:
Monitor closely starting late August for early signs like behavioral changes and vulvar swelling.
Most dogs cycle every 6-8 months (about twice per year). Small breeds may cycle every 4-5 months, while large/giant breeds may only cycle once per year. The interval is typically consistent for each individual dog once they mature.
First heat typically occurs between 6-24 months depending on size. Small breeds often have their first heat around 6-8 months, medium breeds 8-12 months, and large/giant breeds 12-24 months. Some giant breeds don't cycle until 18-24 months old.
The noticeable heat (proestrus + estrus) lasts about 18-21 days total. Proestrus averages 9 days with bloody discharge and swelling. Estrus follows for another 9 days when the female is receptive to breeding. Individual variation is common.
Signs include vulvar swelling, bloody discharge, frequent urination, increased attention from male dogs, behavioral changes (more affectionate or agitated), tail flagging, and mounting behavior. Discharge changes from bloody to straw-colored during estrus.
Yes, dogs can get pregnant during their very first heat cycle, though it's not recommended to breed during the first or even second cycle. Most responsible breeders wait until at least the third cycle and full physical maturity before breeding.
The most fertile period is during estrus, typically days 10-14 of the cycle. Many breeders use progesterone testing or veterinary examination to pinpoint the optimal breeding window, as timing can vary. Ovulation typically occurs days 9-13.
The timing of spaying is debated. Spaying before first heat significantly reduces mammary cancer risk. However, some research suggests waiting until physical maturity (especially for large breeds) may benefit bone and joint development. Discuss with your vet.
No, dogs don't go through menopause like humans. They continue having heat cycles throughout their lives, though cycles may become irregular, less frequent, or less obvious in senior dogs. Older dogs can still get pregnant, though with more risk.
Related Tools
Convert dog years to human years.
Convert between dog and human years.
Predict adult dog size.
Calculate dog life expectancy.
Assess dog health and wellness.
Track dog pregnancy timeline.