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Dog heat cycle calculator
Enter the first day of her last heat to see how long it may last and when her next heat is likely.
The stages of a heat
A heat starts with proestrus: the vulva swells and there is a bloody discharge. Males are interested, but she won’t accept them yet. It lasts about 9 days on average, though anything from about 2 or 3 days to 3 weeks is normal.
Next comes estrus, when she will accept a male and can get pregnant. The discharge often turns lighter or straw-colored, but not always. Estrus also averages about 9 days, with the same wide range. Together the two stages usually last two to three weeks, and sometimes up to six. She can get pregnant from late in proestrus until the heat is fully over.
After that come diestrus, about two months whether or not she is pregnant, and anestrus, a resting phase of usually one to six months, sometimes longer, before the next heat.
| Stage | Typical length | What you see |
|---|---|---|
| Proestrus | About 9 days (2 days to 3 weeks) | Swollen vulva, bloody discharge; males interested but she refuses them |
| Estrus | About 9 days (3 days to 3 weeks) | She accepts males and can get pregnant |
| Diestrus | About 2 months | Heat signs gone |
| Anestrus | Usually 1 to 6 months, sometimes 8 or more | Resting phase before the next heat |
When can she get pregnant?
You can’t tell from the calendar. Ovulation can come anywhere from about 5 to 30 days after the heat starts, so a dog can be fertile early or late in her heat. To avoid a pregnancy, keep her away from intact males until every sign of heat has passed. Spaying is the only certain prevention.
If you plan to breed her, ask your vet about progesterone blood tests. They show when she ovulates, which counting days cannot. Once she’s bred, the dog pregnancy calculator gives the due date.
When is the first heat?
Most dogs have their first heat between 6 and 14 months old. Small breeds can start as early as 4 months, and giant breeds may not start until about 2 years. The first heats are often irregular.
Common questions
How often do dogs go into heat?
Usually about twice a year. The average gap between heats is 6 to 7 months, but anything from about 4 to 13 months can be normal. Some large breeds, such as Great Danes, cycle every 9 to 12 months, and Basenjis and Tibetan Mastiffs usually come into heat only once a year.
How long does a dog stay in heat?
Usually two to three weeks, counting both the bleeding stage (proestrus) and the stage when she will accept a male (estrus). Each averages about 9 days, but each can be as short as 2 or 3 days or as long as 3 weeks.
Can a dog get pregnant when she is not bleeding?
Yes. The bleeding often lightens or stops during estrus, which is when she is most likely to get pregnant. Keep her away from intact males until all signs of heat have passed.
Is this calculator accurate?
It uses average cycle lengths, so treat the dates as a rough guide. Your own dog’s past heats are the best predictor: enter the months between them for a closer estimate. A heat that is very late, very long or comes with illness is worth a call to your vet.
Sources: Davidson AP, “Management of Reproduction in Dogs”, Merck Veterinary Manual (Dog Owners version; reviewed June 2018, updated June 2026). Root Kustritz MV, “Managing the Reproductive Cycle in the Bitch”, Veterinary Clinics of North America: Small Animal Practice 2012;42:423–437, doi:10.1016/j.cvsm.2012.01.012. Dates are estimates from average cycles, not veterinary advice.