Schedules · calculator
Dog Heat Cycle Calculator
Predict your dog's next heat 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 heat expected
Sat, Dec 5, 2026 in about 63 days
- Fertile window of the last heat
- Sun, Jun 14, 2026 to Sat, Jun 20, 2026
- Cycle interval used
- 183 days
| Stage | Days | Dates | What happens |
|---|---|---|---|
| Proestrus | 0–9 | Fri, Jun 5, 2026 to Sun, Jun 14, 2026 | Swollen vulva and bloody discharge. Males are interested; she is not receptive yet. |
| Estrus (fertile) | 9–18 | Sun, Jun 14, 2026 to Tue, Jun 23, 2026 | Discharge lightens to straw-colored. She is receptive and can conceive. This is the fertile window. |
| Diestrus | 18–80 | Tue, Jun 23, 2026 to Mon, Aug 24, 2026 | Receptivity ends. If pregnant, gestation runs through this stage; false pregnancy can also occur. |
| Anestrus | 80–183 | Mon, Aug 24, 2026 to Sat, Dec 5, 2026 | The quiet phase between cycles, lasting until the next proestrus begins. |
Following heat cycles
- Heat 1: Sat, Dec 5, 2026
- Heat 2: Sun, Jun 6, 2027
- Heat 3: Mon, Dec 6, 2027
These are averages. Ovulation timing varies enormously between female dogs and between cycles in the same female dog, and the first two heat cycles 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 heat are counted from day one of visible bleeding.
next heat = 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 female dog 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 heat cycles 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 heat
Assume any intact male within scenting distance will find a way. Walk on a leash, avoid dog parks entirely, and do not leave her unsupervised in a yard that a determined dog could get into. Heat diapers help with mess indoors but prevent nothing.
Watch for signs of pyometra in the weeks after a heat 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 heat in an unspayed female dog.
Common questions
How often do dogs come into heat?
Most female dogs cycle about every six months, so twice a year. Large and giant breeds often go eight to twelve months between heat cycles, 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 heat 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 female dog and that particular cycle.
At what age does the first heat 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 heat 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 heat as risky if you do not want a litter.
Does spaying stop the cycle?
Yes, completely. Timing of spaying relative to the first heat 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.
Reading
- How long are dogs pregnant? 63 days, week by week How long are dogs pregnant? About 63 days from ovulation and remarkably consistent. From the mating date it can look like 57 to 72. Milestones week by week.