Dog Heat Cycle Calculator: When Will My Dog Go Into Heat?

Estimates from average cycle lengths. Individual dogs vary a lot, and only progesterone testing by a vet can pinpoint ovulation. Last reviewed October 7, 2026.

The four stages of a dog's heat cycle

A female dog's cycle has four stages. The part people call "heat" is the first two, which together usually last two to three weeks.

Stage	How long	What you see
Proestrus	About 9 days (3 days to 3 weeks)	Bloody discharge and a swollen vulva. Males are interested, but she won't let them mate.
Estrus	About 9 days (3 days to 3 weeks)	The vulva softens and the discharge often turns watery or pink. She accepts males and can get pregnant.
Diestrus	About 2 months if not pregnant	She refuses males again.
Anestrus	1–6 months	A resting stage with no signs, until the next proestrus.

Stage lengths are from the Merck Veterinary Manual. A dog in heat may also urinate more often and mark objects with small amounts of urine.

How often do dogs go into heat?

The average gap from the start of one heat to the start of the next is about 7 months, and anything from 4 to 13 months can be normal. Size makes a difference: small breeds may cycle up to three times a year, while some giant breeds, such as Great Danes, cycle every 9 to 12 months. Basenjis and Tibetan Mastiffs usually come into heat only once a year.

If your dog's cycles are regular, enter her usual gap above for a more accurate date. Young dogs can take up to two years to settle into a regular pattern.

When is a dog most fertile?

Most dogs ovulate around the 11th day after the first sign of heat, and VCA Animal Hospitals gives days 10 to 14 as the usual best time for breeding. The range is wide, though: some dogs ovulate as early as day 3 or 4, others as late as day 18. Because sperm can survive for about a week, a dog can get pregnant on any day of estrus.

If you don't plan to breed, keep her away from intact males for the whole heat, not just the middle days. If you do plan to breed, your vet can time it with progesterone blood tests. Once she is pregnant, the dog pregnancy calculator gives the due date window.

When do dogs have their first heat?

Most dogs have their first heat between 6 and 24 months of age, and smaller breeds start earlier. Toy and small breeds can have their first heat as early as 4 months, while large and giant breeds may not start until 18 months to 2 years. Dogs do not go through menopause: they keep cycling into old age.

Dog Heat Cycle Explained: How Long and How Often — Save this chart for later or share it with a friend.

Questions people ask

How long does a dog stay in heat?

Usually two to three weeks from the first sign of bleeding. Proestrus and estrus each last about 9 days on average, but either can be as short as 3 days or as long as 3 weeks.

How often does a dog go into heat?

About every 7 months on average, with a normal range of 4 to 13 months. Small breeds may cycle up to three times a year and some giant breeds only once.

When can a dog get pregnant during heat?

During estrus, which usually starts around day 10. Most dogs ovulate around day 11, but it varies a lot, and sperm can survive about a week, so a pregnancy is possible on any day she accepts a male.

Can I predict exactly when my dog will go into heat?

Only roughly. The calculator uses her usual gap if you enter it, otherwise the 7-month average. Keep a note of each heat's start date: after two or three cycles you will know her own pattern.

Do dogs stop having heat cycles when they get old?

No. Dogs don't have menopause, so an unspayed female keeps having heats, and can get pregnant, into her senior years.

Dog heat cycle calculator