Dog Heat Cycle Calculator

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

Cornell’s vet school puts the average gap at six to seven months, with anything from about five to twelve still normal. The AKC (American Kennel Club) says small breeds can cycle three times a year and giant breeds like Great Danes and Irish Wolfhounds once every 12 to 18 months.
The size bands are a starting point. Your own dog’s last two or three cycles beat any table.

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 to about 75)

• Hormone levels drop, female becomes unreceptive
• Lasts about two months whether or not she is pregnant
• If she was mated on days 10–14, puppies are due about 63 days later, so roughly days 72 to 76 counted from the start of heat
• If not pregnant, body may still show signs of “false pregnancy”

Anestrus (About day 76 to next cycle)

• Reproductive rest period, usually four months or more
• No visible signs of cycle

The dates this page prints are the same arithmetic the dog pregnancy calculator uses: mating date plus 63 days. A vet’s progesterone test narrows the whole thing to a single day.

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.