Dog Heat Cycle Calculator
Predict your dog's next heat from her last one, see the four cycle stages mapped onto real dates, and know the fertile window — whether you're planning a litter or planning to avoid one.
Day one = first day of bleeding/swelling
Unknown? 6 months is the safe default
Pick the last heat date to see predictions.
You might also need:Dog Pregnancy Calculator·Dog Age Calculator
How the prediction works
fertile window ≈ days 10–14 of the new cycle
Dogs are individually consistent: whatever her personal rhythm is, she'll roughly keep it. Note the start date of each heat and after two cycles you'll know her interval to within a week or two — far better than any breed average.
The four stages of the cycle
| Stage | Length | Signs |
|---|---|---|
| Proestrus | ~9 days | Swelling, bleeding — males interested, she refuses |
| Estrus | ~9 days | Fertile phase — discharge lightens, she accepts males |
| Diestrus | ~60 days | Cycle winds down (pregnancy occupies this window if mated) |
| Anestrus | 4–5 months | Reproductive rest until the next cycle |
Managing a heat
- Total supervision outdoors: a determined dog (hers or the neighborhood's) makes fences look theoretical. Leash walks only, 3 weeks.
- Dog parks are off: even friendly males become a problem, and she may behave out of character.
- Planning a litter? Progesterone testing at the vet times breeding far better than calendar math — then the dog pregnancy calculator takes over for the 63-day countdown.
- Not planning litters ever? Talk timing of desexing through with your vet.
Frequently asked questions
How often do dogs go into heat?+
Most dogs cycle about every 6–7 months (twice a year). Small breeds can cycle three times a year; giant breeds may only cycle every 8–12 months. Individual dogs are fairly consistent once mature — track two cycles and you can predict the next reliably.
How long does a dog stay in heat?+
The visible heat (proestrus + estrus) lasts about 2–3 weeks. Proestrus (swelling, bleeding, males interested but refused) runs ~9 days; estrus (the fertile phase, when she accepts males) runs another ~9 days, typically days 10–18 from the start.
When is a dog fertile during her heat?+
Peak fertility is usually days 10–14 from the first day of bleeding, during estrus. Sperm survives days and eggs mature over time, so pregnancy is possible from roughly day 7 to day 20 — supervision matters for the entire cycle if you’re avoiding a litter.
At what age do dogs have their first heat?+
Small breeds as early as 6 months, large breeds often 12–18 months, giants up to 2 years. First cycles are frequently irregular and "silent" (minimal signs) — the predictable rhythm settles in by the second or third cycle.
Should I let my dog have a heat before spaying?+
Evidence is mixed and breed-dependent: early spay eliminates heat management and reduces mammary tumor risk, while some large breeds may benefit from maturing first. This is a genuinely good question for your vet — the answer differs by breed, size and lifestyle.