How the due date window is worked out
Dog pregnancies are counted from one of three reference points, and the Merck Veterinary Manual gives a different range for each. The calculator adds those days to your date and shows the whole window rather than one date, because a single date would look more certain than the science is.
| Counting from | Whelping after | How you get the date |
|---|---|---|
| First day she accepted breeding | 58–72 days | You saw it |
| LH surge or progesterone rise | 64–66 days | Blood tests during the heat |
| First day of diestrus | 56–58 days | Vaginal cytology (smears) during the heat |
Earliest = reference date + shortest days
Latest = reference date + longest days
Worked example
A dog first bred on October 1, 2026: October 1 + 58 days = November 28, and October 1 + 72 days = December 12. So puppies are most likely between November 28 and December 12. If the vet's progesterone test had put the LH surge on October 1 instead, the window would shrink to December 4–6.
Why the breeding date gives a two-week window
Breeding is not conception. Sperm can live in the female for several days, and her eggs need a couple of days to mature after ovulation, so the pregnancy can start some days after mating. That is why Merck says breeding dates and conception dates do not line up closely enough to predict whelping. Hormone timing narrows it: Merck's breeding chapter puts whelping 64–66 days after the LH peak.
Getting ready
- Ask your vet about confirming the pregnancy and, close to term, about an x-ray to count puppies so you know when she is finished.
- Take her rectal temperature twice a day for the last week or so. Merck notes that most dogs drop to 36.7–37.8 °C (98.1–100 °F) 8 to 24 hours before whelping.
- Ask your vet ahead of time which signs during labor they want you to call about, and save the number of the nearest 24-hour emergency clinic.
- Call your vet if she passes the end of the window, or if she has a temperature drop and no labor, seems ill, or has a green or bloody discharge before any puppy arrives.
Sources checked October 2026.
Questions people ask
How long is a dog pregnant?
About two months, but the exact count depends on where you start. The Merck Veterinary Manual gives 58 to 72 days from the first day the female accepted breeding, 64 to 66 days from the LH surge or first rise in progesterone, and 56 to 58 days from the first day of diestrus. The often-quoted 63 days is a rough middle.
Why is the window so wide from a breeding date?
Because mating and conception are not the same day. Sperm can survive in the female for days and her eggs need time to mature after ovulation, so a breeding date can be well before or after the day the pregnancy actually started. Merck notes that breeding dates do not predict whelping closely.
How can I get a more exact due date?
Ask your vet about progesterone testing during the heat (to find the LH surge or progesterone rise) or vaginal cytology to find the first day of diestrus. Either narrows the window to about 3 days. Your vet can also confirm the pregnancy and check fetal maturity near term with ultrasound or x-rays.
What are the signs labor is close?
A drop in rectal temperature is the classic sign: Merck says most dogs drop to 36.7–37.8 °C (98.1–100 °F) 8 to 24 hours before whelping. Many dogs also become restless, start nesting and go off their food. Take her temperature twice a day in the last week so you know her normal.
What if my dog goes past the due date?
Call your vet once she is past the end of the window, or sooner if she has had a temperature drop but no labor, seems unwell, or has a green or bloody discharge before any puppy arrives. Merck warns against waiting too long, because puppies can die in the uterus.