Most female dogs come into heat (also called “in season”) about every six to seven months, though anything from four to twelve months can be normal. Enter the first day of her last heat to predict the next ones.
Dog Heat Cycle Calculator
Predict your dog’s next seasons and the likely fertile days.
The four stages of a dog’s heat cycle
Proestrus (about 9 days): the vulva swells and there is bloody discharge; males are interested but she will not accept them. Estrus (about 9 days): discharge lightens and she will accept a mate — this is the fertile phase. Diestrus (about 2 months): her body behaves as if pregnant whether she is or not. Anestrus: a resting phase until the next cycle.
Do dogs have periods? Not in the human sense — the bleeding happens before ovulation, not after it. Read our guide to dog periods.
Frequently asked questions
How long does a dog stay in heat?
Usually two to three weeks in total.
At what age do dogs have their first heat?
Around six months on average — from about 4 months in some small breeds to 18–24 months in some giant breeds.
Can I predict exactly when my dog is fertile?
Not from dates alone. Fertile days vary a lot between dogs; if you are planning a breeding, your vet can time it with progesterone blood tests.