How this calculator works
Merck lists 114 days as an approximate pig gestation. Without a herd-specific distribution this tool shows the same default earlier and later marker rather than suggesting a verified safety window. Supply your herd veterinarian's lower and upper planning limits when known. 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 114 days, with a 114 to 114 day planning window. Days remaining = due date - observation date. The window is not a guarantee.
Worked example
A sow bred on 1 January 2026 has a 114-day estimate of 25 April. On 15 January, 14 days have elapsed and 100 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.