A simple worked method for estimating a due date by hand, following the same logic described in calculating the due date — use it alongside your vet’s own assessment, not instead of it.
The most important first
- The most accurate estimate is 63 days from confirmed ovulation, not from the mating date.
- Use progesterone or LH surge data if you have it; fall back to mating date only if you don’t.
- Treat any calculated date as an estimate window, not a guaranteed day.
Free interactive tool
Prefer not to count by hand? Our calculator works out the whole window from ovulation, LH, progesterone or mating dates, and builds a plan you can print or add to your calendar. Open the due date calculator →
If you have ovulation data
Take the date your vet identified as ovulation (from progesterone testing) and add 63 days. If what you have is an LH-surge date, add about 65 days instead (ovulation follows the LH surge by about two days), and if it is the first rise in progesterone, add 64–66 days. With hormone-timed dates, most bitches whelp within a day or two of the estimate. This is the most reliable estimate available, and the date to build your whelping preparation checklist timeline around.
Example: Ovulation confirmed 2 September → estimated due date 4 November (63 days later).
If you only have a mating date
Add 63 days to the mating date as a rough starting estimate, but treat it as considerably less reliable — potentially off by a week or more in either direction, since it doesn’t account for how long sperm may have survived before ovulation actually occurred. If a mating spanned several days (repeat matings), count from the earliest date so your preparation starts early enough, and the estimate as a whole should be refined as pregnancy progresses.
Example: Mating observed 30 August to 1 September → adding 63 days gives central dates of 1–3 November, but that is not the whole window. Counting from the first mating, whelping anywhere from about 27 October to 10 November (roughly 58–72 days) would still be normal, so prepare for the early end of that range and start taking her temperature about a week before it.
Refining the estimate as pregnancy progresses
An early ultrasound (from around three to four weeks after breeding) can confirm the pregnancy and viability, and fetal measurements taken at around four weeks can also narrow the due date considerably, especially when you only have a mating date. If you want that refinement, ask your vet to measure the puppies at the scan rather than leaving imaging until late, because late-pregnancy measurements are much less accurate for dating. The skeleton shows on X-ray from about days 42–45, but an X-ray in the last week or so (from about day 55) is mainly for counting puppies and checking maturity, such as whether their teeth have formed, rather than for pinpointing the date. Whatever your starting estimate, treat the final two weeks before it as the active preparation window described in preparing for whelping, rather than waiting for a single calculated day.
If the date passes
If she is more than a couple of days past a hormone-timed date (about day 66 from the LH surge), or reaches about 70 days from the first mating with no labor, call your veterinarian rather than waiting. Puppies can be lost in an overdue pregnancy.
When to call your vet
- She is past about day 66 from the LH surge, or about 70 days after the first mating, with no labor.
- Her temperature has dropped and labor has not started within 24 hours of the drop.
- Green or black discharge before the first puppy — this is an emergency, call your vet immediately.
- She has a fever above 103 °F (39.5 °C) or seems unwell late in pregnancy.
- If in doubt, call — your vet would rather hear from you early.
Work on it
A few minutes here will teach you more than re-reading the article.
Ask yourself
- Am I using ovulation data for this estimate, or only a mating date?
- Have I treated the result as a window, not a single guaranteed day?
Find out & check
- Find out whether your vet can help refine the estimate using ultrasound or X-ray findings as pregnancy progresses.
Do one thing
- Calculate your estimated due date now using the method above, and set your whelping-preparation start date two weeks earlier.
Was this article helpful?
Anonymous. We do not store your name, email or IP address.
Sources & further reading
- Merck Veterinary Manual (Davidson AP) — Breeding Management of Bitches. merckvetmanual.com
- Siena G, Milani C (2021), Animals 11(3):878 — Usefulness of Maternal and Fetal Parameters for the Prediction of Parturition Date in Dogs. pmc.ncbi.nlm.nih.gov
- Concannon PW (2000), IVIS — Canine Pregnancy: Predicting Parturition and Timing Events of Gestation. ivis.org
- Lopate C (2008), Theriogenology 70:397–402 — Estimation of gestational age and assessment of canine fetal maturation using radiology and ultrasonography: a review. cdn.ymaws.com
- Kutzler MA et al. (2003), Theriogenology 60(7):1309–1317 — Accuracy of canine parturition date prediction using fetal measurements obtained by ultrasonography. experts.umn.edu
- Cornell University, Riney Canine Health Center — The Normal Whelping Process. vet.cornell.edu
- Merck Veterinary Manual — Whelping and Queening in Bitches and Queens. merckvetmanual.com
- American Kennel Club — How Long Are Dogs Pregnant? Dog Gestation Period. akc.org
Where evidence is limited, recommendations rest on established practice and expert judgment, and may be updated as knowledge develops.
Next steps
- Related: Calculating the due date · Preparing for whelping: the final two weeks.
- Return to the area hub: Pregnancy: managing the pregnant bitch week by week.
- This completes Area 5 — Pregnancy & the Pregnant Dam (12/12 articles).