Dog Heat Cycle Calculator — Next Season Predictor

Formula

How this is calculated

The canine oestrous cycle has four stages. Proestrus (roughly the first 9 days) is marked by a bloody vaginal discharge and swelling; the female attracts males but is not yet fertile. Estrus (approximately days 9–18) is the fertile window during which the female will accept mating — ovulation typically occurs on days 10–14. Diestrus follows whether or not mating occurred, lasting 60–90 days (this is why an unmated bitch can have a "false pregnancy"). Anestrus is the quiet resting period that makes up the remainder of the inter-oestrous interval.

The interval between heat cycles varies considerably by individual and breed: most dogs cycle every 5–7 months (the default here is 180 days), small breeds can cycle as often as every 4 months, and giant breeds such as the Great Dane and Mastiff may cycle only once a year. Track your dog's actual dates over two or three cycles to calibrate the figure.

This calculator gives estimated dates only. Actual ovulation timing requires progesterone blood tests and/or vaginal cytology performed by a vet — critical for planned breeding or for avoiding unwanted pregnancy at the right stage. The fertile window shown here is a statistical average and can shift by several days in any individual dog.