The short answer
| Counted from | Average | Normal range |
|---|---|---|
| Ovulation | 63 days | 62 to 64 days |
| LH surge peak | 65 days | 64 to 66 days |
| A single mating date | 63 days | 56 to 70 days |
In weeks that is nine, and in months a little over two. The pregnancy is divided into three trimesters of about three weeks each.
Why the range is so wide from mating
Dog sperm can survive in the female tract for several days, and her eggs need two to three days after ovulation to mature. So conception can happen days after mating. Two dogs mated on the same day can deliver a week apart and both be normal.
Hormone testing removes most of this uncertainty. When ovulation is confirmed by progesterone testing, whelping is far more precise, usually within a day of day 63.
What else changes gestation length
- Size of breed. Toy and small breeds tend to deliver slightly early, giant breeds slightly late.
- Litter size. Very large litters often start labor a day or two early; a single puppy may arrive late or need help.
- Dating method. The biggest factor of all, as above.
See the litter size by breed table for typical litters.
When a long pregnancy is a problem
Call your vet if she is more than a couple of days beyond day 65 from ovulation with no signs of labor, or if she passes day 70 from mating. Puppies born before about day 57 from ovulation are premature and need immediate veterinary help.