One of the most frequently asked questions about female dogs is when they can get pregnant. It all depends on when they first go into heat—otherwise known as the estrous cycle. This is the dog equivalent to human menstruation.

You won’t see anywhere near as much blood, but you may notice a little, as well as swelling in the vulva area (and probably a few male dogs hanging around your yard).

Dogs usually go into their first estrous cycle around six months old, although it could be as late as 14 months. After that, they go into heat every six to eight months, for about three weeks each time on average. The most fertile days in that cycle are between days 11 and 15.

If your dog’s in heat, be very careful on walks! She’ll let any male dog mount her—and the scent of her urine will draw those dogs back to your house. To avoid that risk, talk to your vet about getting her spayed.

Some vets spay as early as six weeks of age. If you don’t get her spayed, she could get pregnant at any age, although her fertility will decline a little as she gets older. That’s right; there’s no menopause for dogs. Book the procedure, expect multiple litters, or quarantine her during estrous. The choice is yours to make!