Dog Heat Cycle Calculator
Work out your dog’s likely fertile days and predict her next heats from the first day of her season.
Most likely fertile days
Oct 1, 2026 – Oct 10, 2026
Treat her as able to get pregnant from Sep 27, 2026 until every sign of heat is gone (usually by Oct 13, 2026, sometimes Oct 20, 2026).
- Next heat 1, around
- Apr 22, 2027 (± about a month)
- Next heat 2, around
- Nov 22, 2027 (± about a month)
- Next heat 3, around
- Jun 22, 2028 (± about a month)
Fertile days vary a lot between dogs. Only progesterone tests at your vet pin down ovulation.
How we calculate this: the formula, its sources and its limits
Quick answer
Count from the first day of swelling or bleeding. A dog is most likely fertile on about days 10 to 19, but can get pregnant from about day 6 until every sign of heat has gone, usually after 2 to 4 weeks. Most dogs come back into heat every 6 to 7 months.
How do I use the dog heat cycle calculator?
- Enter the first day you noticed her vulva swelling or a bloody discharge.
- Choose how often she comes into heat. If you don’t know, leave the 7-month average.
- Read her most likely fertile days and the date the heat should be over.
- Note the predicted dates of her next heats, and update them once you have logged a few real ones.
What formula does the heat cycle calculator use?
Could be fertile: from day 6 until all signs stop (day 22–29)
Next heat ≈ first day + interval (average 7 months, range 4–13)
The stage lengths (about 9 days of proestrus and about 9 days of estrus) are from VCA Animal Hospitals; the 7-month average and 4–13 month range are from the Merck Veterinary Manual. These are averages: individual dogs vary a lot, which is why the calculator shows a cautious wider window too.
How is the calculation done?
Using an example first day of heat:
- Day 1 is the first day you notice swelling or bloody discharge: Mon, Mar 2, 2026.
- Proestrus lasts about 9 days (days 1–9, to Mar 10, 2026). She attracts males but usually won’t let them mate.
- Estrus, the fertile and receptive phase, lasts about 9 more days: days 10–19, Mar 11, 2026 to Mar 20, 2026.
- Because some dogs ovulate early or late, treat her as fertile from day 6 (Mar 7, 2026) until all signs stop, usually by day 22–29 (Mar 23, 2026–Mar 30, 2026).
- Add the interval between heats (here the 7-month average) for the next one: about Oct 2, 2026, give or take a month.
What are the four stages of a dog’s heat cycle?
| Stage | Typical length | What you’ll see |
|---|---|---|
| Proestrus | About 9 days (3–17) | Swollen vulva, bloody discharge, attracts males but refuses them. |
| Estrus | About 9 days (2–24) | Discharge turns lighter or straw-colored; she flags her tail and accepts males. Ovulation happens early in this stage. |
| Diestrus | About 2 months | No longer receptive. Pregnant or not, hormones behave like pregnancy, which is why false pregnancies happen. |
| Anestrus | About 4 months (varies) | Resting phase until the next heat. |
For the signs at each stage in more detail, read how long a dog is in heat.
Example heat calendar
For a dog whose heat started on Mon, Mar 2, 2026 and who cycles every 7 months:
| Event | Date |
|---|---|
| Proestrus ends (about day 9) | Mar 10, 2026 |
| Most likely fertile days | Mar 11, 2026 to Mar 20, 2026 |
| Heat usually over | Mar 23, 2026 to Mar 30, 2026 |
| Next heat 1 | around Oct 2, 2026 |
| Next heat 2 | around May 2, 2027 |
| Next heat 3 | around Dec 2, 2027 |
If she was mated, when are the puppies due?
Dogs are pregnant for about 63 days. Enter the mating date in our dog pregnancy calculator for the due date and the 58–72 day window, and read how to tell if your dog is pregnant for the signs to watch for. A mother can come back into heat a few months after a litter; how soon a dog can get pregnant after giving birth covers the timing.
When should I call the vet about her heat?
- A heat that lasts more than about 4 weeks, or heats less than 4 months apart.
- No heat at all by 24 months of age.
- Pus-like or foul-smelling discharge, heavy drinking, a swollen belly or lethargy in the weeks after a heat. These can be signs of pyometra, a womb infection that is an emergency.
- You want to breed her: ask about progesterone testing to time mating.
If you don’t plan to breed, ask your vet about the best age to spay her. Spaying ends heat cycles and removes the risk of pyometra.
Frequently asked questions
How do I calculate my dog’s fertile days?
Count from the first day of swelling or bleeding. The receptive, fertile phase usually runs from about day 10 to day 19, but some dogs ovulate as early as day 5 or as late as day 25. For planned breeding, progesterone blood tests at your vet are the only reliable way to time it.
How often do dogs go into heat?
Most dogs cycle about twice a year. Merck gives an average of 7 months between heats, with a normal range of 4 to 13 months. Small breeds often cycle more often and giant breeds less often; Basenjis usually cycle once a year.
How long does a dog’s heat last?
Usually 2 to 4 weeks from the first sign to the last, often around three. The bleeding stage lasts about 9 days, then comes about 9 days when she is receptive. The discharge often lightens just as she becomes most fertile.
Can I predict my dog’s next heat exactly?
Not exactly. Each dog has her own rhythm, and the gap can drift by weeks. Log two or three heats, then set the interval in the calculator to her own average for a better forecast.
When does a puppy have her first heat?
Usually around 6 months, but anywhere from 6 to 24 months is normal. Small breeds tend to start early, while large and giant breeds may not cycle until 18 months to 2 years.
Can a dog get pregnant when she is not bleeding?
Yes. Her most fertile days often come after the bleeding has eased, and sperm can survive in her for about a week. Keep her away from intact males until every sign of heat has gone.
Sources
- VCA Animal Hospitals. Estrous cycles in dogs (proestrus and estrus each about 9 days; estrus range 2–24 days; first heat timing). vcahospitals.com
- Merck Veterinary Manual, Pet Owner Version. Management of reproduction in dogs (interval between heats average 7 months, range 4–13). merckvetmanual.com
- Cornell University College of Veterinary Medicine, Riney Canine Health Center. Dog estrous cycles (first heat 6–24 months; stage lengths). vet.cornell.edu
Vet disclaimer: These are estimates for healthy pets. Your vet knows your pet. Ask them before changing diet or care, especially for puppies, kittens, seniors, pregnant pets or pets with health conditions. Read our medical disclaimer.