Dog Heat Cycle Calculator
Calculate your dog's next heat cycle date, best breeding window, and current heat phase.
Based on breed size and last heat start date.
Dog Heat Cycle (Estrus)
Female dogs (bitches) experience a reproductive cycle called estrus, commonly known as “heat.” Unlike cats (which cycle continuously in breeding season), dogs cycle roughly twice a year — though this varies significantly by size.
Cycle Frequency by Breed Size
| Breed Size | Weight | Avg Cycle | Range |
|---|---|---|---|
| Small | Under 20 lbs | Every 5 months | 4–6 months |
| Medium | 20–50 lbs | Every 6 months | 5–7 months |
| Large | 50–100 lbs | Every 10 months | 8–12 months |
| Giant | Over 100 lbs | Every 12 months | 10–16 months |
Giant breeds like Great Danes and Irish Wolfhounds may only cycle once per year.
The Four Phases
Proestrus (Days 1–9)
- Swelling of vulva, bloody discharge
- Attracts males, but female is not ready to mate
- Duration: 7–10 days (average 9)
Estrus (Days 10–14)
- Discharge becomes lighter or straw-colored
- Female is receptive to males — ovulation occurs
- Best breeding window: days 10–14
- Duration: 5–9 days
Diestrus (Days 15–60)
- Hormone levels drop, female becomes unreceptive
- If pregnant, gestation begins (~63 days)
- If not pregnant, body may still show signs of “false pregnancy”
Anestrus (Day 61 to next cycle)
- Reproductive rest period
- No visible signs of cycle
When to Spay
Spaying before the first heat greatly reduces risk of mammary tumors. Each heat cycle increases the risk. Consult your vet for the right timing.