Dog heat calculator: when is her next season?
This dog heat calculator predicts when your female dog will next come into heat (season) from the first day of her last one, and lays out the four stages of the cycle — proestrus, estrus, diestrus and anestrus — on real dates. It also marks where she is in the cycle today and gives an estimate of her most fertile days.
Most dogs come into season about every seven months, but the normal range is wide: from about four to thirteen months between heats, and some breeds such as the Basenji and Tibetan Mastiff cycle only once a year. Each dog tends to keep her own rhythm, so the best prediction comes from her own history — enter the start of the heat before her last one and the calculator uses that interval.
Everything here is a typical pattern from the Merck Veterinary Manual and Cornell University’s canine health centre. Use it to plan walks, boarding and neutering appointments; for breeding, ask your vet about progesterone testing.
How to use the Dog Heat Cycle Calculator
- Enter the first day of her last heat — the first day you saw swelling or bloody discharge.
- Choose the time between heats: the 7-month average, twice a year, once a year, your own number, or work it out from her previous heat.
- Adjust the proestrus and estrus lengths if you know them; 9 days each is average.
- Read the next heat date, the two after it and the stage she is in today on the ring.
- Check the stage table for dates and what you will see in each stage.
Dog Heat Cycle Calculator features
Next three heats
Predicted start dates of the next three seasons from her interval.
Four stages on a calendar
Proestrus, estrus, diestrus and anestrus dates for her current cycle.
Animated cycle ring
Each stage drawn to scale with a marker on today.
Her own rhythm
Enter her previous heat and the calculator uses her personal interval.
Estimated fertile days
Clearly marked as an estimate from published averages, not a test result.
The four stages of a dog’s heat cycle
Source: Merck Veterinary Manual, “Breeding Management of Bitches” (reviewed June 2025; checked October 2026). Cornell’s canine health centre gives proestrus as 6–11 days and estrus as 5–9 days on average, and says bloody discharge usually lasts 14–21 days in total. The “heat” or “season” owners notice is proestrus plus estrus — about three weeks.
| Stage | Typical length | What happens |
|---|---|---|
| Proestrus | 9 days (3 days – 3 weeks) | Swelling, bloody discharge, attracts males but refuses them |
| Estrus | 9 days (3 days – 3 weeks) | Accepts mating; LH surge and ovulation |
| Diestrus | About 2–3 months | Refuses males; pregnancy-like hormones whether pregnant or not |
| Anestrus | 1–6 months | Rest until the next heat |
How the next heat is predicted
The calculator adds the interval in calendar months to the first day of her last heat: 1 January plus 7 months is 1 August, then 1 March and 1 October of the next year. Half months add about 15 days. When you enter two heats, the gap between them, in months, becomes the interval.
Fertile days are estimated as days 3–6 after the start of estrus, following Merck’s advice to breed three to six days after the LH surge. With a 9-day proestrus that is days 13–16 counted from the first day of bleeding. The real fertile period can come much earlier or later, which is why breeders and vets use progesterone blood tests rather than calendars.
First heat, spaying and when to call the vet
Cornell reports that most dogs have their first heat between 6 and 24 months of age, small breeds earlier than large ones. If you plan to spay, ask your vet about timing — many prefer to wait until about three months after a heat. If she is mated by accident, call your vet promptly; to estimate a due date use the dog pregnancy calculator. Planning a litter? Check the relationship of the parents with the coefficient of inbreeding calculator.
Call your vet if a heat lasts much longer than usual, if she has discharge between heats, or if she becomes quiet, thirsty or off her food in the weeks after a heat — these can be signs of pyometra, a womb infection that needs urgent treatment.
Dog Heat Cycle Calculator FAQ
How often do dogs come into heat?
About every seven months on average, with a normal range of roughly four to thirteen months. Most dogs have two heats a year; Basenjis and Tibetan Mastiffs usually have one.
How long is a dog in heat?
The visible heat — proestrus plus estrus — usually lasts about three weeks. Bloody discharge typically lasts 14–21 days, though each stage can be as short as 3 days or as long as 3 weeks.
How does a dog heat calculator predict the next season?
It adds her usual interval, 7 months by default, to the first day of her last heat. If you enter the heat before that, it uses the gap between them instead.
When is a female dog most fertile?
Usually around the middle of the heat, a few days after estrus begins. This calculator estimates days 3–6 after the start of estrus, but only progesterone testing can tell you reliably.
Can a dog get pregnant outside heat?
No — only during estrus. But sperm can survive for over a week, so mating late in proestrus can still lead to pregnancy.
Is this veterinary advice?
No. Ask your vet — this is general information, not veterinary advice, and the stages shown are typical rather than measured for your dog.