What this calculator does
Estimate an animal due date or breeding date from a typical gestation period.
How it works
The calculator evaluates due date = breeding date + gestation days; breeding date = due date − gestation days. Inputs are checked before calculation, and invalid values such as zero denominators or out-of-range selections produce a clear error instead of a misleading result.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
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?animal=AnimalChoice · Required · Default: cow · Accepted values: cow, pig, sheep, goat, horse, chicken, quail, dog, cat, rabbit, guineaPig, hamster, ferret, elephant, custom
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?mode=CalculateChoice · Required · Default: due · Accepted values: due, breeding
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?date=Known dateDate · Required · Default: 2026-09-01
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?customDays=Custom gestation period (days)Number · Required · Default: 150
Outputs
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resultDateEstimated dateDate · Primary output
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gestationDaysGestation periodWhole number · Suffix: days
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gestationWeeksApproximate weeksNumber
Inputs and results
The inputs are Animal, Calculate, Known date, Custom gestation period (days). Results include Estimated date, Gestation period, Approximate weeks.
Important notes
This educational estimate does not replace veterinary care. Gestation varies by animal, breed, litter, and health.