Dog Heat Cycle Calculator
When is your dog most fertile, and when is her next heat due? Enter the first day of her last heat and her breed size for an estimate.
Enter the first day of her last heat to estimate the windows.
Estimates only — cycles vary a lot, and young dogs are often irregular. For planned breeding, your vet can pinpoint ovulation with progesterone testing. To avoid an accidental litter, keep an unspayed female away from intact males for the whole 2–3 weeks of heat.
Estimate only — not veterinary advice. Every animal is different; for a medication dose, a possible poisoning, or any emergency, call your veterinarian or an animal poison control line right away.
How the estimate works
This tool counts forward from the first day of her last heat. The most fertile window — roughly days 9 to 14, when ovulation usually happens — is highlighted, and the next heat is projected using the typical interval for her breed size. Because cycles vary, treat the dates as a planning guide rather than a guarantee.
Planned vs accidental litters
If you're trying to breed, this gives you a target window, but your vet can pinpoint ovulation with progesterone testing for the best timing. If you're trying to avoid a litter, remember a female can be fertile for several days and males are determined — keep them fully separated for the whole 2–3 weeks. Spaying removes the heat cycle (and several health risks) entirely; the cost calculator can help you budget for it.
Frequently asked questions
- How often do dogs go into heat?
- Most dogs come into heat about twice a year, but it varies with size: small breeds often every 6 months, larger breeds every 7–8, and some giant breeds only once a year. Young dogs and some breeds (like Basenjis) can be different again. The calculator estimates the next cycle from the interval for your dog's size.
- How long does a dog's heat last?
- The visible heat lasts about 2 to 3 weeks. It runs through proestrus (swelling and bleeding, she's not yet receptive) into estrus (the fertile phase, when bleeding lightens and she'll accept a male), then winds down. Keep an unspayed female away from intact males for the whole period to avoid an accidental litter.
- When is a dog most fertile?
- Usually around days 9 to 14 of the cycle — a few days into estrus, when most dogs ovulate and are receptive. That's the window this calculator highlights. It's an estimate, though: the exact fertile days shift between dogs and cycles, so for planned breeding a vet uses progesterone tests to time it precisely.
- What are the signs my dog is in heat?
- A swollen vulva, a bloody or straw-colored discharge, more frequent urination and marking, restlessness or clinginess, and male dogs taking sudden interest. Some dogs keep themselves very clean, so the first sign owners notice is the attention from males.
Sources
These are the references behind this calculator. Where a source gives a range we take the midpoint and round toward caution, and where we go beyond what a source states — an extra safety margin, or a rule of thumb rather than a clinical threshold — the page says so in the text above.
- Estrus and mating in dogs — VCA Animal Hospitals