Free Dog Heat Cycle Calculator
A dog heat cycle calculator estimates when your unspayed female dog will next be in heat, using the start date of her last heat and her usual interval. Most dogs cycle about every six months, so the dates are a planning guide, not a guarantee.
Your dog's heat dates
Nothing you enter is saved or sent anywhere.
Heat cycle forecast
Enter the first day of her last heat to see her next estimated heat dates.
During and after each heat
- Preventing pregnancy: keep her on a leash outdoors and away from intact males from the first sign of heat until all swelling and discharge have stopped. Supervise her closely; males can track a female in heat.
- Planning a breeding: these dates are only a starting point. Ask your veterinarian about progesterone testing to time ovulation; calendar day counts are not reliable.
- After heat, call your veterinarian promptly if she drinks or urinates much more, has vaginal discharge, a swollen belly, lethargy, vomiting, or stops eating. These can be signs of pyometra, a serious uterine infection.
- Contact your veterinarian as soon as possible if she may have mated unintentionally, and ask about heats that seem unusually long or irregular, or no first heat by about 2 years old (large and giant breeds can take that long).
How to use the calculator
- Enter the first day of her last heat, when you first saw swelling or bloody discharge.
- Add the start of the heat before that to use her own interval, or choose a typical interval for her size.
- Review her current heat stage, next estimated heat dates, likely fertile stage, and post-heat watch window.
- Print the forecast for your calendar, your sitter, or your veterinarian, and update it when her next heat starts.
Dog heat cycle FAQ
How often do dogs go into heat?
Most dogs come into heat about every six months, or twice a year. Small breeds may cycle three times a year, while giant breeds may cycle only once a year. Each dog's interval can differ, so her own records give the best estimate.
How long is a dog in heat?
Proestrus averages about 9 days and estrus, the fertile stage, averages about 9 more, but each stage can last 3 to 21 days. This calculator uses the averages and marks them as estimates.
When is a dog most fertile during heat?
She is fertile during estrus, which usually starts around the time her discharge becomes lighter and watery. Ovulation timing varies, so breeders use veterinary progesterone testing rather than a fixed day count. She can become pregnant at any point in estrus.
How old is a dog at her first heat?
On average about six months, though toy breeds can start at 4 to 5 months and large or giant breeds may not have a first heat until 18 months to 2 years. Dogs can become pregnant during their very first heat.
What should I watch for after my dog's heat?
Watch for drinking or urinating more, vaginal discharge, a swollen belly, lethargy, vomiting, or loss of appetite. These can signal pyometra, a serious uterine infection that can occur 2 to 16 weeks after a heat. Contact your veterinarian promptly.
Sources and calculation notes
Stage lengths come from the AKC guide to how long dogs are in heat: proestrus and estrus each average about 9 days and can range from 3 to 21 days; it also recommends progesterone testing to time breeding. Cycle frequency and first-heat ages come from VCA's estrus cycles in dogs. The post-heat watch window uses VCA's pyometra guidance (2 to 16 weeks after a heat). Checked November 8, 2026.
Next heat = last heat start + interval. A typical interval is months × 30.44 days, rounded; a measured interval is the day count between her last two heat start dates. Fertile stage = day 10, heat end = day 18, watch-for-signs = 14 days before. Estimates already past are skipped. This is general information, not veterinary advice; no data is saved or sent.