Dog Heat Cycle Calculator

How the calculator works

The best predictor of a dog's next heat is her own history. If you have recorded two or more heats, enter the average number of days between them. Otherwise the calculator uses typical intervals for her size, then marks a window about a month either side, because healthy dogs vary.

To work it out by hand, count forward from the first day of her last heat – about six months for most medium and large dogs. For a heat that began on 1 March 2026, a six-month interval points to around 30 August 2026.

The four stages of a dog's heat cycle

Owners usually call proestrus and estrus together 'the heat' or 'season'. It typically lasts two to three weeks from the first sign of bleeding.

How often dogs go into heat

Some breeds, such as the Basenji, typically cycle only once a year. Cycles can also be irregular during the first year or two. A 'silent heat' – ovulation with few visible signs – is common in young dogs, and a 'split heat' can stop and restart a few weeks later.

Signs your dog is coming into heat

• Licking her rear end more often and a slightly swollen vulva, sometimes a few days before bleeding.
• More frequent urination and marking on walks.
• Clinginess, restlessness or irritability with other female dogs.
• Male dogs suddenly showing much more interest in her.

Fertile window and ovulation

Most dogs ovulate around 9–12 days after the start of proestrus, but this varies widely – some ovulate as early as day 5 or as late as day 20 or more. Eggs need a couple of days to mature after ovulation, and sperm can survive in the female tract for several days. For planned breeding, vets use blood progesterone tests to pinpoint ovulation; for avoiding pregnancy, keep her away from intact males for the whole heat, about three weeks.

Spaying, pyometra and when to call the vet

Many vets prefer to spay two to three months after a heat has ended, when blood supply to the uterus has returned to normal; ask yours about the best timing for her age and breed. Unspayed females have a significant lifetime risk of pyometra, a serious uterine infection – Swedish insurance data found about 1 in 4 intact females affected by 10 years of age. It often appears weeks after a heat.

• Heat bleeding lasting more than about 3–4 weeks.
• No heat by 24 months of age, or more than 12 months between heats in a small or medium dog.
• Pus-like or foul-smelling discharge, drinking much more than usual, vomiting, a swollen belly or lethargy – especially in the weeks after a heat (possible pyometra – an emergency).

Caring for your dog during heat

• Walk her on a lead only, at quieter times, and avoid dog parks for the whole heat.
• Keep her indoors or supervised in a securely fenced garden – males can travel surprisingly far.
• Use washable dog-heat pants or cover bedding if bleeding is heavy.
• Expect mood changes; give her a quiet space and keep routines normal.

Tracking her cycles

Write down the first day of bleeding or swelling each time, plus the day the discharge stops. After two or three cycles you will know her personal interval, which is far more accurate than a breed-size average. Enter that interval in the calculator for future predictions.

Sources

1. Merck Veterinary Manual – Reproductive cycle of the bitch — merckvetmanual.com
2. VCA Animal Hospitals – Estrus cycles in dogs — vcahospitals.com
3. Egenvall A. et al. (2001) Breed risk of pyometra in insured dogs in Sweden, J Vet Intern Med — doi.org/10.1111/j.1939-1676.2001.tb01586.x