Dog Heat Cycle Calculator – Predict Your Dog's Next Heat
Enter the first day of her last heat to estimate when her next heat will start, how long it will last, and the typical fertile days in each cycle.
Disclaimer: Calendar estimates can’t tell you when your dog ovulates or guarantee she is fertile. For planned breeding, ask your vet about progesterone testing.
How the heat cycle calculator works
Most dogs come into heat about twice a year, roughly every 6 months. The calculator adds your dog’s usual cycle length to the first day of her last heat to predict her next three heats. For each one it shows the commonly cited fertile days (days 9–14) and when the heat usually ends (about 3 weeks after it starts).
These are calendar averages. Dogs can ovulate earlier or later than average, and cycle lengths can change. If you’re planning a breeding, your vet can time it with progesterone blood tests and vaginal cytology. They’re far more reliable than any calendar.
The 4 stages of a dog's heat cycle
| Stage | How long | What you'll notice |
|---|---|---|
| Proestrus | About 9 days (3–17) | Swollen vulva and bloody discharge. Males are interested, but she usually won't let them mate. |
| Estrus | About 7–10 days | Discharge often gets lighter. She may flag her tail and accept a male. Ovulation happens around day 2 of estrus on average, so this is the fertile stage. |
| Diestrus | Up to about 2–3 months | She stops accepting males. Hormones are similar whether or not she's pregnant, so false pregnancy can happen. |
| Anestrus | About 4 months on average | A resting stage with no signs of heat until the next cycle starts. |
How often do dogs go into heat?
Most unspayed female dogs come into heat about twice a year. Some breeds, such as Basenjis and Tibetan Mastiffs, usually cycle only once a year. Small breeds often cycle a little more often, and giant breeds less often.
The first heat usually happens between 6 and 12 months of age, about 2–3 months after a dog reaches her adult size. Some small breeds start as early as 4 months, while some sighthounds don’t have their first heat until after 2 years.
How long does a dog stay in heat?
A dog’s heat usually lasts about 2 to 3 weeks. The bleeding stage (proestrus) and the fertile stage (estrus) together typically last 12 to 20 days.
When is a dog most fertile?
Dogs are fertile during estrus, the second stage of heat. On average they ovulate around the second day of estrus, often somewhere around days 9–14 after the first sign of heat. Timing varies a lot between dogs, and even between cycles in the same dog. Some ovulate as early as day 5, others well after day 20.
That’s why responsible breeders use progesterone testing. A vet measures progesterone every few days as heat progresses to pinpoint ovulation and the best breeding days. Once she’s mated, use our dog pregnancy calculator to work out her due date.
Signs your dog is coming into heat
- Swollen vulva
- Bloody or pink discharge, and more licking of the area
- Peeing more often or marking
- Restless, clingy or moody behavior
- Male dogs suddenly very interested in her
When to call your vet
- She hasn’t had a heat by about 2 years of age.
- Heats come less than 4 months apart, or bleeding lasts much longer than 3 weeks.
- She has pus-like or foul-smelling discharge, drinks a lot, or seems unwell in the weeks after a heat. These can be signs of pyometra, a serious uterine infection that needs urgent care.
- You’re planning a breeding and want to time it accurately.
Dog heat cycle FAQs
Can a dog get pregnant when she isn't bleeding?
Yes. The discharge often gets lighter or turns straw-colored during estrus, which is when most dogs are fertile. Lighter bleeding doesn't mean the heat is over.
How long after bleeding starts is a dog fertile?
On average, dogs are most fertile around days 9–14 after the first sign of heat. But some dogs ovulate much earlier or later, so progesterone testing is the only reliable way to know.
Do dogs go through menopause?
No. Female dogs keep having heat cycles for life, although cycles can become less regular as they age. An unspayed older dog can still get pregnant.
Why is my dog's heat cycle irregular?
Irregular cycles are common in young dogs during their first year or two of heats. If cycles stay irregular, come less than 4 months apart, or stop, talk to your vet.
How accurate is a dog heat cycle calculator?
It's a planning tool. It adds your dog's usual cycle length to her last heat date, so it works best when you enter her real, recent dates. Each dog's cycle can change by a few weeks.
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Open calculator →Sources: GoodRx Pet Health – How Long Are Dogs in Heat? (reviewed by Ghanasyam Bey, DVM); Merck Veterinary Manual. This page is general information, not veterinary advice. Read our veterinary disclaimer.