Dog Heat Cycle Predictor
Predict your dog's next season from her cycle history, with the fertile window and each stage of the cycle dated.
The first day you saw bleeding, not the day the swelling started.
Typically twice a year.
Next season expected
Thu, 12 Nov 2026 in about 63 days
- Fertile window of the last season
- Fri, 22 May 2026 to Thu, 28 May 2026
- Cycle interval used
- 183 days
| Stage | Days | Dates | What happens |
|---|---|---|---|
| Proestrus | 0–9 | Wed, 13 May 2026 to Fri, 22 May 2026 | Swollen vulva and bloody discharge. Males are interested; she is not receptive yet. |
| Estrus (fertile) | 9–18 | Fri, 22 May 2026 to Sun, 31 May 2026 | Discharge lightens to straw-colored. She is receptive and can conceive. This is the fertile window. |
| Diestrus | 18–80 | Sun, 31 May 2026 to Sat, 1 Aug 2026 | Receptivity ends. If pregnant, gestation runs through this stage; false pregnancy can also occur. |
| Anestrus | 80–183 | Sat, 1 Aug 2026 to Thu, 12 Nov 2026 | The quiet phase between cycles, lasting until the next proestrus begins. |
Following seasons
- Season 1: Thu, 12 Nov 2026
- Season 2: Fri, 14 May 2027
- Season 3: Sat, 13 Nov 2027
These are averages. Ovulation timing varies enormously between bitches and between cycles in the same bitch, and the first two seasons of a young dog are often irregular. If you are planning a mating, progesterone testing is the only reliable way to time it.
How this is calculated
Prediction is simply the last known start date plus the typical interval for that size group. The stages within the season are counted from day one of visible bleeding.
next season = last start + cycle interval
proestrus days 0 to 9 not receptive
estrus days 9 to 18 receptive and fertile
diestrus days 18 to 80 receptivity ends
anestrus day 80 onward quiet phase until the next cycle Typical interval by size
| Size group | Interval | Notes |
|---|---|---|
| Small breed | 6 months | Often cycle every 5 to 6 months. |
| Medium breed | 6 months | Typically twice a year. |
| Large breed | 8 months | Often only every 8 months. |
| Giant breed | 12 months | Some giant breeds cycle once a year. |
Why these are averages, not predictions
Cycle length is an individual characteristic. A bitch who reliably cycles every seven months will keep doing so, and the useful interval for her is her own history, not a table. Once you have two or three recorded start dates, use the average gap between them rather than the size group default.
Sources
- Merck Veterinary Manual. Breeding Management of Bitches (estrous cycle and gestation).
- Johnston SD, Root Kustritz MV, Olson PNS. Canine and Feline Theriogenology. Philadelphia: WB Saunders; 2001. Standard reference text for canine gestation length and whelping. No free full text.
Keep a record
Write down the first day of bleeding every time. Two or three recorded seasons give you a personal interval that is far more accurate than any breed average, and a sudden change in that interval is itself useful information, since irregular cycles can point to ovarian or thyroid problems.
Managing a season
Assume any intact male within scenting distance will find a way. Walk on lead, avoid dog parks entirely, and do not leave her unsupervised in a garden that a determined dog could get into. Season pants help with mess indoors but prevent nothing.
Watch for signs of pyometra in the weeks after a season ends: increased drinking, lethargy, loss of appetite, or any discharge. It is a surgical emergency and it typically appears four to eight weeks after a season in an unspayed bitch.
Common questions
How often do dogs come into heat?
Most bitches cycle about every six months, so twice a year. Large and giant breeds often go eight to twelve months between seasons, and some primitive breeds cycle only once a year. Any regular interval from four to twelve months can be normal for the individual.
How long does a dog stay in heat?
The visible season lasts about two to three weeks. Proestrus, with swelling and bloody discharge, runs roughly nine days, followed by around nine days of estrus when she is receptive and fertile.
When is a dog most fertile?
Usually days 9 to 15 counting from the first day of bleeding, but this is an average and ovulation timing varies enormously. If you are planning a mating, progesterone testing is the only reliable way to identify the window for that particular bitch and that particular cycle.
At what age does the first season happen?
Typically six to twelve months in small breeds and up to two years in giant breeds. The first two or three cycles are often irregular or silent, so predictions based on them are unreliable.
How do I know the season has finished?
Swelling subsides and discharge stops, usually after about three weeks. Keep her away from intact males for a full week after everything looks normal, because receptivity can outlast the visible signs.
Can a dog get pregnant outside the fertile window?
Mating outside the window rarely results in pregnancy, but sperm survive up to a week in the reproductive tract, so a mating several days before ovulation can still conceive. Treat the entire season as risky if you do not want a litter.
Does spaying stop the cycle?
Yes, completely. Timing of spaying relative to the first season is a real discussion to have with your vet: it affects mammary tumour risk, and in some large breeds it affects joint disease and certain cancers. There is no single right answer across all breeds.