How Long Is a Dog in Heat? Stages, Bleeding and Fertile Days

How long is a dog in heat? Usually about three weeks, though anything from two to four is normal. The part that catches people out is the middle: the bleeding gets lighter right around the time she’s most fertile. We’ve laid out each stage with the vet numbers, then used our dog pregnancy calculator to show what an accidental mating mid-season would mean.

What are the stages of a dog’s heat cycle?

Vets split the cycle into four stages. Only the first two are what most of us call “in heat.”

Stage	How long (average)	Normal range	What you’ll see
Proestrus	About 9 days	2 days to 3 weeks	Swollen vulva, bloody discharge, males interested but she says no
Estrus	About 9 days	2 to 24 days (VCA)	Discharge turns pinkish, watery or straw-colored; she’ll accept a male and may flag her tail to one side
Diestrus	About 2 months		Swelling goes down; phantom pregnancy can show up here
Anestrus	1 to 6 months		Quiet phase before the next heat

The averages and ranges come from Merck and VCA. Cornell gives slightly tighter typical figures: proestrus 6 to 11 days and estrus 5 to 9 days.

How long does a dog bleed in heat?

Here the sources disagree, and we’d rather show you than pick one. The Royal Kennel Club says most dogs bleed for about 7 to 10 days. Cornell says bloody discharge usually lasts 14 to 21 days. In practice it depends on the dog, and a tidy dog who licks a lot may look like she barely bleeds at all.

What matters more is the color change. VCA and the Royal Kennel Club both say ovulation tends to happen around when the discharge turns watery. Since sperm can survive about a week, a mating a few days before she ovulates can still lead to puppies.

How often do dogs go into heat?

Question	Typical answer	Source
First heat	About 6 months; 6 to 24 months is normal	VCA, Cornell
Large and giant breeds	May not start until 18 to 24 months	VCA
Time between heats	Average 7 months (range 4 to 13)	Merck
Heats per year	Usually two; small breeds up to three, giants maybe one	VCA
Once-a-year breeds	Basenji, Tibetan Mastiff	Cornell

First heats are often irregular. VCA says it can take up to two years for a young dog’s cycles to settle. Our puppy weight calculator can help you guess her adult size class, which hints at whether she’s likely to start early or late, and when do puppies stop growing explains why big dogs mature later.

Worked example: a three-week season, day by day

Take a 2-year-old, 12 kg cocker spaniel whose bleeding starts on March 1, 2027. Using the average stage lengths:

Dates	Likely stage	What to do
Mar 1 to about Mar 9	Proestrus	Leash walks only, quiet times of day
About Mar 10 to Mar 18	Estrus, the fertile window	Strictest separation from intact males; don’t leave her alone in the yard
About Mar 19 to Mar 22	Signs fading	Keep the rules until swelling and discharge have fully stopped

Now say a neighbor’s dog got to her on March 12. Enter that as the “Breeding date” in the pregnancy calculator and it gives an average due date of May 14, 2027, with a window of May 9 to May 23. The calculator also dates the vet checks, and our post on how to tell if your dog is pregnant explains which test to book when. If this happens to you, call your vet within a few days. They can talk you through options, which are time-sensitive.

With a 7-month average gap, her next season would land around October 2027, but don’t plan your life around that. Anything from 4 to 13 months can be normal.

Do older dogs still go into heat?

Yes. The Royal Kennel Club points out that dogs don’t go through menopause, so an older unspayed dog can still get pregnant, even if her heats spread further apart. Our dog age calculator shows that an 8-year-old, 25 kg dog is about 55 in human years. Pregnancy at that age carries more risk, which is why the Royal Kennel Club usually won’t register litters from dams over 8.

When should I spay my dog after heat?

VCA says most vets recommend spaying before 6 to 7 months, while some large breeds may benefit from waiting. If she’s already had a heat, Cornell suggests waiting about 2 months after it ends, because the uterus takes time to shrink back. Spaying stops heats, prevents pyometra and reduces the risk of mammary cancer. Your vet will help you weigh the timing for her breed.

When to call your vet

Call your vet if:

• She was mated by accident. Options are time-sensitive.
• Her heat signs last more than about 40 days. Merck says this can point to ovarian cysts.
• She’s had no heat by 24 months, or seems to cycle much more often than every 4 months.
• She bleeds heavily enough to seem weak, or bleeds when she isn’t in heat.
• In the weeks after a heat she’s tired, drinking a lot, vomiting, off her food or has a smelly discharge. These are signs of pyometra, a womb infection that needs urgent treatment. Merck says it usually shows up 4 to 6 weeks after heat, mostly in dogs over 5.
• A phantom pregnancy (milk, nesting, mothering toys) lasts more than about three weeks.

If she does turn out to be pregnant, the week-by-week pregnancy guide and how many puppies will my dog have are good next reads.