Meddor
How often?
According to the Merck Veterinary Manual, the interval between two heats ranges from 4 to 13 months, 7 months on average. Heats come all year round, with no season. That’s why your dog’s own rhythm is the most reliable guide: note the date each heat starts.
The first heat comes between 6 and 24 months of age: earlier in small breeds, later in large ones.
How long it lasts
| Phase | What you see | Length |
|---|---|---|
| Proestrus | Bloody discharge, swollen vulva. She attracts males but doesn’t accept them yet. | 7 to 10 days of discharge |
| Estrus | She accepts a male. Discharge may lessen. | 9 days on average, 3 to 21 |
Ovulation usually happens 1 to 3 days after estrus begins. Sperm can survive nine days or more: a mating before the fertile window can still lead to a pregnancy.
What about cats?
Cats are different: during the season, from spring to early autumn, heat comes back every 2 to 3 weeks and lasts 6 to 7 days. A cat ovulates when she’s mated. Her first heat comes between 4 and 12 months. You’ll recognise it by her behaviour: rolling, rubbing, kneading and loud yowling.
Frequently asked questions
My dog is expecting puppies: when will they arrive?
Our pregnancy calculator gives you the due-date window from the mating date.
Her heats are irregular
According to Merck, a dog can differ from the average without being ill, and only a vet can tell whether her cycle is abnormal. Tell them what you’ve noted: the dates will help.
Should I have her spayed?
That’s a decision to make with your vet, who knows your dog and can explain the benefits and risks for her age and breed.
Sources
- Merck Veterinary Manual, “Breeding Management of Bitches”, July 2025: interval between heats, estrus length, sperm survival.
- Merck Veterinary Manual, “Features of the Reproductive Cycle”: puberty, cycle, discharge, ovulation, cats.
- Merck Veterinary Manual, “Management of Reproduction of Cats”, August 2025: behaviour of a cat in heat.