If you purposely bred your dog, calculate 63 days from the breeding date to figure out an approximate due date. That's the average canine gestation period, although some dogs give birth a few days earlier or later. If you don't know when your dog got pregnant, you must rely on veterinary expertise and your dog's physical signs.
As your dog's due date approaches, watch for the changes that indicate whelping -- the term for canine labor -- is near. Start taking her temperature every morning and evening with a rectal thermometer. A dog's normal temperature ranges between 101 and 102 degrees. Once it drops below 100 degrees, expect the puppies to arrive within 24 hours. A few days before whelping, you might notice her belly dropping. When labor begins, your dog might become restless and clingy. She'll show no interest in food.
During her pregnancy, your dog should receive prenatal care from your vet. When your dog is in her sixth week of pregnancy, your vet can take an X-ray of the abdomen to see how many puppies you can expect. At that point, the puppies' skeletons have mineralized so they can be viewed on the X-ray. Your vet can give you an estimated due date if you are uncertain of the breeding dates.