How this calculator works
The default uses 65 days. VCA describes a 60 to 67 day gestation range, while Merck lists 65 days as an approximate period. Multiple matings make the starting date uncertain. Date arithmetic uses whole calendar days in UTC, so daylight-saving changes do not shift the result. A negative elapsed value means the reference date is still ahead; a negative remaining value means the estimate has passed.
Formula
Due date = reference date + assumed gestation days. Reverse mode subtracts the same duration. The default is 65 days, with a 60 to 67 day planning window. Days remaining = due date - observation date. The window is not a guarantee.
Worked example
A mating on 1 January 2026 gives an estimate of 7 March, with a planning window from 2 to 9 March. On 15 January, 14 days have elapsed and 51 remain to the estimate.
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Frequently asked questions
Does the estimated date confirm pregnancy?
No. A recorded mating may not result in pregnancy. Veterinary examination and appropriate imaging are needed for confirmation.
Can I work backwards from a due date?
Yes. Choose breeding-date mode. The answer is the date implied by the assumed duration, not proof of the actual conception day.
Why might birth occur outside the window?
Breeding and ovulation dates can differ, and litter size, breed and individual history influence timing. Arrange monitoring with your veterinarian instead of using the window as a safety test.