Dog Heat Cycle Calculator
Enter the first day of your dog’s last heat to see when the next one is likely and a calendar of this heat, from proestrus to the end.
The day you first noticed bleeding. Sometimes the discharge isn’t noticed until several days in (VCA).
Enter the first day of her last heat to see when the next one is likely.
This calculator only estimates – no calendar works as birth control. Keep her away from intact males for the whole heat and at least a week after the bleeding stops (Dogs Trust).
Why only roughly?
The time between two heats averages 7 months, and 4 to 13 months is normal (Merck). Small breeds may come into heat up to three times a year, giant breeds sometimes only once (VCA), and Basenjis and Tibetan Mastiffs once a year (Cornell). The heat itself varies too: ovulation can fall anywhere from day 5 to day 30 (Root Kustritz, University of Minnesota). Only your vet can pin down the fertile days, with progesterone tests and vaginal cytology (smears) (Freie Universität Berlin). Keeping males away until day 35 is our own estimate – no source names that day: a heat usually lasts up to 4 weeks (PDSA, Dogs Trust), plus at least a week after the bleeding stops (Dogs Trust). If she’s still bleeding or males are still interested, keep them away longer.
When to call your vet
- The heat lasts longer than 40 days (Merck).
- White discharge during her heat (PDSA).
- Usually 4 to 8 weeks after a heat: drinking a lot, vomiting, a swollen belly, lethargy, poor appetite or pus-like discharge – there may be no discharge at all. This can be a uterine infection (pyometra): an emergency, call right away (PDSA).
- Her heats keep coming at irregular intervals (PDSA) – in young dogs this is often normal for up to two years (VCA).
- An unplanned mating happened: call as soon as possible – some injections only work in the first few days (Royal Kennel Club).
The short answer
Most female dogs come into heat every 6 to 7 months (PDSA); the average interval is 7 months, and 4 to 13 months is normal (Merck). A heat lasts about 18 days: roughly 9 days of proestrus and 9 days of estrus (Freie Universität Berlin). Example: a heat starting November 1, 2026 – estrus around November 10–18, the next heat most likely around June 1, 2027, usually between about May 1 and July 1, 2027 – though anywhere from March to December 2027 (4 to 13 months) is normal.
Questions
How often do dogs go into heat?
Usually every 6 to 7 months (PDSA), 7 months on average; 4 to 13 months is normal (Merck). Small breeds may come into heat up to three times a year, giant breeds sometimes only once (VCA), and Basenjis and Tibetan Mastiffs once a year (Cornell).
How long does a dog’s heat last?
About 18 days: roughly 9 days of proestrus and 9 days of estrus (Freie Universität Berlin). It can last 2 to 4 weeks (Dogs Trust). Sources differ on the bleeding: usually 7 to 10 days (Dogs Trust) or 14 to 21 days (Cornell). When the discharge turns watery and lighter, she’s often at her most fertile (VCA).
When is a dog most fertile?
Estrus starts after about 9 days of proestrus on average (Freie Universität Berlin). The best time to breed is usually 11 to 13 days after the heat begins, but it varies a lot (Freie Universität Berlin) – ovulation can fall anywhere from day 5 to day 30 (Root Kustritz). Only your vet can pin it down, with progesterone tests and vaginal cytology (smears).
When does a dog have her first heat?
Cornell gives 6 to 24 months. Small breeds come earlier, some as early as 4 months (Root Kustritz); large and giant breeds later, some not until two and a half years (PDSA).
Do dogs stop going into heat when they get older?
No, dogs don’t go through menopause. The gaps between heats usually get longer, but she can still get pregnant (PDSA).
How long should I keep her away from male dogs?
For the whole heat (PDSA) and at least a week after the bleeding stops; if males are still interested, longer (Dogs Trust). Heat diapers won’t reliably stop a mating (Royal Kennel Club).
When does a false pregnancy happen?
Usually 6 to 8 weeks after a heat (PDSA). It usually goes away on its own within 1 to 3 weeks (Merck). If you’re worried, check with your vet.
Related
- Dog pregnancy calculatorEnter the date of the first breeding to see when the puppies are due. If your vet pinpointed ovulation, the date gets more precise.
- Feeding after spaying or neuteringAfter spaying or neutering, dogs and cats need less energy. If you don’t adjust the amount, it often shows on the scale a few months later.
- Dog food calculatorDaily amount for your dog – from weight and your food.
Sources (12)
- Merck Veterinary Manual (Pet Owner Version): Management of Reproduction in Dogs
- Merck Veterinary Manual (Pet Owner Version): Reproductive Disorders of Female Dogs
- Freie Universität Berlin, Small Animal Clinic: Cycle disorders in the bitch (in German)
- Freie Universität Berlin, Small Animal Clinic: Timing of breeding (in German)
- PDSA – Seasons in dogs
- PDSA – Pyometra (infected womb) in dogs
- PDSA – Phantom pregnancy in dogs
- Dogs Trust – Everything you need to know if your dog is in heat
- Cornell Riney Canine Health Center: Dog estrous cycles
- Root Kustritz MV (2012): Managing the Reproductive Cycle in the Bitch. Vet Clin North Am Small Anim Pract 42:423–437 (University of Minnesota)
- VCA Animal Hospitals – Estrous Cycles in Dogs
- The Royal Kennel Club – Your dog’s seasons