Free Dog Heat Cycle Calculator
This dog heat cycle calculator predicts your dog's next heat and fertile days. Enter the first day of her last heat.
The four stages of a dog's heat cycle
| Stage | Length | What you see |
|---|---|---|
| Proestrus | about 9 days (3–17) | Swollen vulva and bloody discharge. Males are interested but she will not accept them yet. |
| Estrus | about 9 days (3–21) | Discharge lightens. She accepts males; ovulation usually happens early in this stage. |
| Diestrus | about 2 months | The heat is over, whether or not she is pregnant. |
| Anestrus | about 4 months | A resting phase until the next heat. |
How the dog heat cycle calculator works
- This heat ends: about 21 days after it started (usually 14–28).
- Fertile days: typically days 9–14 of the heat.
- Next heats: the first day plus your chosen interval, repeated.
Young dogs often have irregular cycles. If a heat lasts more than about 4 weeks, or there is pus-like discharge, lethargy or heavy drinking after a heat, see a vet promptly. Planning a litter? Use the dog pregnancy calculator once she is bred.
Frequently asked questions
How does the dog heat cycle calculator work?
It counts forward from the first day of the last heat: the heat itself usually lasts about 3 weeks, the most fertile days are typically days 9 to 14, and the next heat comes after the interval you choose (6 months for most dogs).
How often do dogs go into heat?
Most dogs come into heat about twice a year, roughly every 6 months. Small breeds can cycle up to three times a year, and giant breeds may go 12 months or more between heats.
How long does a dog stay in heat?
Usually 2 to 4 weeks, about 3 weeks on average, counting from the first sign of swelling or bleeding.
When is a dog most fertile?
Typically around days 9 to 14 of the heat, but it varies a lot between dogs and between cycles. Progesterone blood tests from your vet are the reliable way to time breeding.
When do dogs have their first heat?
Usually between 6 and 15 months of age; small breeds earlier, and giant breeds sometimes as late as 18 to 24 months.