Enter the first day of your dog’s last heat and get an estimate of when the next one is due, plus a dated timeline of the heat she may be in now. Every dog is different and the dates below are estimates. If you are planning a litter, your vet can time ovulation accurately with a blood test.
Count day 1 as the first day you saw swelling or bloody discharge. If this is her first heat, keep the default gap and treat the next date as a rough guide.
How the dog heat cycle works
A female dog’s heat cycle has four stages. Proestrus is the lead-up, with a swollen vulva and bloody discharge, and lasts about 9 days on average. Estrus follows, when she is receptive to males, also about 9 days on average. Diestrus comes next and lasts roughly two months, whether or not she is pregnant. Anestrus is the quiet gap before the next cycle begins. Counting proestrus and estrus together, most heats last about two to four weeks.
How often do dogs go into heat?
Most dogs come into heat about every six months, although the gap can be anywhere from four to twelve months. A few breeds, such as the Basenji, typically cycle once a year. A first heat usually happens between six and twelve months of age. Large and giant breeds can be later, sometimes between 18 and 24 months. The first few cycles are often irregular, which is why the next-heat date here is shown as a range.
Why a calendar cannot pinpoint ovulation
Ovulation can happen as early as day 5 or as late as day 25 after the first sign of bleeding, and it varies between dogs and between cycles in the same dog. Eggs stay fertile for about two to three days, and sperm can live for several days inside the female. That is why breeders and vets rely on progesterone blood tests, often with vaginal cytology, to time mating or insemination. If you plan a litter, a vet visit before the heat starts is the right first step, including breed health testing and a check that she is mature enough. Many vets and breed clubs advise waiting until at least the second or third heat.
When to call your vet
Call promptly if a heat lasts much longer than three weeks, if the bleeding is very heavy, or if she seems unwell. In the weeks after a heat, watch for signs of pyometra, a womb infection that is most common in the one to three months after estrus: unusual lethargy, extra drinking and urination, vomiting, loss of appetite, a swollen belly, or pus-like discharge. This is an emergency.
Frequently asked questions
How long does a dog stay in heat?
Most dogs are in heat for about two to four weeks. The receptive part, estrus, usually lasts around nine days but can range from three to twenty-one.
Can a dog get pregnant while she is bleeding?
Yes. Pregnancy is possible at any point during the heat, so keep her away from intact males until it is completely over.
When should I spay my dog?
The best timing depends on her breed, size and health, and current veterinary guidance changes. Ask your vet when to spay rather than relying on a fixed age. If you want to plan around a heat, our Dog Pregnancy Calculator covers what happens if she is bred.
This tool offers general estimates based on typical canine reproductive cycles and does not replace advice from your veterinarian. Last reviewed: 5 October 2026.