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PawCurve

Dog pregnancy calculator

Every other calculator asks for the breeding date and adds 63 days. That answer is about two days early, and it hides a sixteen-day window. This one asks which date you actually have.

Which date do you have?

This is the question that decides everything. The anchors are not interchangeable — the same pregnancy gets a 3-day window from an LH surge and a 16-day one from a breeding date.

Why "breeding date + 63" is wrong twice

It's the most repeated number in dog breeding, and it fails in two separate ways at once.

1. It's biased about 2 days early.

The 63-day figure is real — but it belongs to ovulation, not to the breeding date. Ovulation happens roughly 2 days after the LH surge, so "65 days from the LH surge" and "63 days from ovulation" are the same fact told from two different starting lines. Moving the 63 onto the breeding date without adjusting is the error. Measured from the day of first mating, Concannon's own mean was 65.3 days.

2. It implies a precision nobody has ever measured.

Canine sperm stay fertile for days after mating — Concannon demonstrated fertile matings 3 days before the LH peak, concluding sperm survive "at least 6 days". So the breeding date isn't the conception date, and it can't be. Across 290 pregnancies the interval from first mating to whelping ranged from 57 to 72 days. Any single date drawn from a breeding date is a point estimate wearing a costume.

The four anchors, and what each is worth

Same pregnancy, four starting lines, wildly different precision. This is the table the "+63" calculators leave out.

Counting fromWhelpingRangeRange is…Source
LH surge65 days64–66 (3 d)publishedConcannon et al. 1983, Am J Vet Res 44(10):1819-21 (n=54)
Progesterone rise65 days62–68 (7 d)publishedKutzler et al. 2003, Theriogenology 60(6):1187-96 (n=63)
Ovulation63 days62–64 (3 d)derivedTsutsui et al. 2006, Theriogenology 66(6-7):1706-8 (n=36)
Breeding date65 days57–72 (16 d)publishedConcannon et al. 1983, Am J Vet Res 44(10):1819-21 (n=290)

"Published" means the range appears in the paper. "Derived" means we computed it and are telling you so. The ovulation range is derived from the LH range, because no study publishes one for that anchor.

What Concannon et al. 1983 actually says about the lh surge anchor
"The interval from the day of the peak in luteinizing hormone (LH) to parturition was less variable and ranged from 64 to 66 days and averaged 65.1 ± 0.1 days (n = 54)."

— Concannon et al. 1983, Am J Vet Res 44(10):1819-21

What Kutzler et al. 2003 actually says about the progesterone rise anchor
"the accuracy of parturition date prediction within a ±1, ±2, and ±3 day interval using prebreeding serum progesterone concentrations was 67, 90, and 100%, respectively, and that the accuracy was not affected by body weight or litter size."

— Kutzler et al. 2003, Theriogenology 60(6):1187-96

What Tsutsui et al. 2006 actually says about the ovulation anchor
"Gestation length (interval from ovulation to parturition) was almost constant at 63.9 ± 0.2 days (mean ± S.E.M.)"

— Tsutsui et al. 2006, Theriogenology 66(6-7):1706-8

We show 63 while the quote above says 63.9 — that gap is real and worth explaining rather than hiding. Tsutsui dated ovulation as the day plasma progesterone passed 2 ng/mL; the LH-anchored arithmetic (65 minus the 2 days from surge to ovulation) gives 63. It is a disagreement about how to date ovulation, not about dogs. The 62-64 window covers both, and no study publishes a range for this anchor — that window is our arithmetic from the LH range, not a published figure.

What Concannon et al. 1983 actually says about the breeding date anchor
"apparent gestation length, estimated as the interval from the day of first mating to the day of parturition, ranged from 57 to 72 days, and averaged 65.3 ± 0.2 days"

— Concannon et al. 1983, Am J Vet Res 44(10):1819-21

Even the AKC contradicts itself on this

We didn't go looking for this. While checking sources we found the American Kennel Club publishing both answers, on its own site, about the same quantity.

Their breeding article — correct

Lists all four anchors properly: "65–66 days from LH surge", "63 days on average from ovulation (2 days after LH surge)", and "58–72 days from the first time the bitch allowed breeding".

Their chief veterinary officer's page — the bare myth

"she will deliver puppies approximately 63 days after breeding" — the wrong number against the wrong anchor, with no window at all.

We're not scoring points. It shows how deep the "+63" habit runs: it survives inside the institution whose own breeding article gets it right. If you've been given a single confident due date from a mating date, this is probably why.

Two authorities are unambiguous about it. Merck's veterinary manual: "Breeding dates and conception dates do not correlate closely enough to permit accurate prediction of whelping dates." UC Davis: "Predicting whelping dates from breeding dates is imprecise."

What we deliberately left out

Two knobs you'll see elsewhere are missing here, and their absence is the considered answer rather than an oversight.

  • No breed or size selector. We hold breed data — it powers our other calculators — so adding one would be easy. But no source supports a size rule, and the best study found small terriers gestating longer than German Shepherds. A dropdown here would look like precision and deliver none.
  • No litter-size input. The effect is about a day, and it doesn't survive within-breed analysis — the authors who found the correlation say so themselves.

The source that argues against us

We should show you this rather than quietly skip it. The same Merck manual we quote approvingly above also states: "Breed, parity, and litter size can also influence gestational length." That cuts against leaving both knobs out.

Our reasoning for standing pat: Merck gives no citation for that sentence, and the primary studies underneath it don't add up to something calculable. Breed effects are real — we cite them — but they don't line up with size, which is the only thing a dropdown could offer. Parity has been tested directly and found not to matter (Seki 2010: 64.3 days for first-timers vs 64.2 for experienced bitches). "Can influence" is true and still not enough to compute with.

The practical summary: which date you count from swamps all of these by an order of magnitude. That's why it's the variable this calculator asks for.

Frequently asked questions

How long are dogs pregnant?
It depends entirely on what you count from — and that's not a technicality, it's the whole answer. From the LH surge it's 65 days and remarkably tight: Concannon et al. (1983) measured a range of just 64–66 days across 54 pregnancies. From ovulation it's about 63, because ovulation happens roughly 2 days after the LH surge. From the breeding date the same study measured 57 to 72 days across 290 pregnancies — a 16-day spread, averaging 65.3. Those aren't competing claims; they're one fact measured from four different starting lines.
Is my dog's due date 63 days after breeding?
No — and this is the most common error on the internet. It's wrong twice. First, it's about 2 days early: Concannon's measured mean from the day of first mating was 65.3 days, not 63. The 63 belongs to a different anchor (ovulation) and gets moved onto the breeding date without adjusting. Second, it implies a precision nobody has ever measured — from a breeding date the real range is 57–72 days. The reason is simple biology: sperm stay fertile for days, so mating and conception aren't the same event. Merck's veterinary manual puts it flatly: "Breeding dates and conception dates do not correlate closely enough to permit accurate prediction of whelping dates."
Why do breeders pay for progesterone testing?
Because it buys precision that no amount of calendar arithmetic can. The spread from a breeding date is roughly 4.7× wider than from the LH surge (comparing the studies' own variability figures). Kutzler et al. (2003) timed 63 pregnancies across 19 breeds from the initial progesterone rise and predicted whelping to ±1 day in 67% of cases, ±2 days in 90%, and ±3 days in 100%. Compare that with needing a ±7-day window to cover the breeding-date range. That gap is what you're buying.
Does breed or size change the length of pregnancy?
Published studies do not support a reliable breed-size adjustment, so the calculator uses the variable that matters most: which date you are counting from. The intuition is that bigger dogs gestate longer, but Okkens et al. (2001) found the opposite: West Highland White Terriers (small) gestated longer than German Shepherds and Labradors. A different study (Eilts 2005) used one anchor for some breed groups and a different anchor for others, so its groups cannot be compared directly. We have not found a sourced, monotonic size rule suitable for a calculator.
Does litter size affect the due date?
Barely, and not reliably enough to calculate with. Larger litters are associated with slightly shorter pregnancies — Eilts (2005) put it at about one day between small and large litters. But the effect largely dissolves under scrutiny: Okkens et al. (2001), who found a strong correlation across their whole sample, state that within each breed, regression "failed to show any influence of litter size on the duration of gestation" — meaning the correlation was mostly a between-breed artefact. Tsutsui (2006) and Seki (2010) found no relationship at all. A ~1-day effect that doesn't survive within-breed analysis doesn't belong in a calculator.
Where do these numbers come from?
Primary literature, read and quoted rather than repeated: Concannon et al. (1983), Am J Vet Res 44(10):1819-21 for the LH and breeding-date anchors; Tsutsui et al. (2006), Theriogenology 66(6-7):1706-8 for ovulation; Kutzler et al. (2003), Theriogenology 60(6):1187-96 for progesterone timing and its measured accuracy. The 2-day surge-to-ovulation offset is from De Lesegno et al. (2008). Every window on this page is labelled as either published or our own arithmetic — we don't blur the two.

Related

Sources last checked 2026-07-17. Concannon P, Whaley S, Lein D, Wissler R. Canine gestation length: variation related to time of mating and fertile life of sperm. Am J Vet Res 1983;44(10):1819-21 (PMID 6685444). Tsutsui T, et al. Relation between mating or ovulation and the duration of gestation in dogs. Theriogenology 2006;66(6-7):1706-8 (PMID 16494933). Kutzler MA, et al. Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration. Theriogenology 2003;60(6):1187-96 (PMID 12935856). De Lesegno CV, et al. Mol Reprod Dev 2008 (PMID 17476693). Okkens AC, et al. J Reprod Fertil Suppl 2001;57:193-7 (PMID 11787149). Eilts BE, et al. Theriogenology 2005;64(2):242-51 (PMID 15955350). Seki M, et al. Can J Vet Res 2010;74(1):78-80 (PMID 20357965). Institutional quotes fetched from the Merck Veterinary Manual, the AKC and UC Davis Veterinary Medicine. Full detail on our methodology page.