CollarDog Heat Cycle Calculator: Next Season & Fertile Window
Track your dog's heat cycle. Estimate when her next season is due and when her fertile window falls, from the start date of her last heat and her breed size.
Dog Heat Cycle Calculator
Enter the start of her last heat to estimate her cycle.
How the Dog Heat Cycle Works
A dog's reproductive cycle, or "season", moves through distinct phases. Knowing where she is helps you plan a breeding or simply prepare for her next heat.
The Four Phases
- Proestrus (about days 1 to 9): bleeding begins and her vulva swells, but she is not yet receptive to males.
- Estrus (about days 9 to 18): the fertile phase. She is receptive and can become pregnant; the most fertile days are usually days 9 to 15.
- Diestrus (about 2 months): the fertile window closes, whether or not she is pregnant.
- Anestrus: the resting phase between cycles, until the next season.
Canine Heat Cycle: How Often She Cycles
Most dogs come into heat about every 6 months, but this depends on breed size, so this calculator adjusts the interval accordingly.
Note the start of her heat
Record the first day you saw bleeding or swelling.
Add her breed size
Cycle length varies between small and giant breeds.
See her cycle
Get her next expected season and the fertile window of this heat.
Frequently Asked Questions
Answers to the most common questions about the canine heat cycle.
Most dogs go into heat about twice a year, roughly every 6 months. Small breeds may cycle more often (every 4 to 6 months), while some giant breeds cycle only once a year. A young dog's cycle can be irregular during her first year or two.
A visible heat lasts about 2 to 4 weeks. It has two main phases: proestrus (roughly the first 9 days, with bleeding but she is not yet receptive) and estrus (roughly days 9 to 18, when she can become pregnant).
A dog is usually most fertile during the estrus phase, around days 9 to 15 after the start of her heat, though this varies from dog to dog. The only reliable way to pinpoint the fertile window and ovulation is progesterone testing at your vet.
Yes. Small breeds tend to come into heat more frequently, sometimes every 4 to 6 months. Medium and large breeds usually cycle about every 6 to 7 months. Giant breeds often cycle only once every 12 months.
A canine heat cycle calculator estimates when a dog's next season is due and where her fertile window falls. You enter the first day of her last heat and her breed size, and it applies the average canine cycle interval to project the next one. Only a progesterone test at your vet can confirm ovulation.
Sources & Further Reading
The cycle figures on this page reflect published veterinary averages. To go deeper, visit these trusted references: