About This Calculator
This site exists to answer one question quickly and accurately: when is this animal due? Breeders, smallholders, dairy and beef producers, stud managers and pet owners all need the same thing, a due date they can plan around, plus an honest picture of how wide the normal range is.
Who runs this site?
Animal Gestation Calculator is an independent reference site. It is not owned by a veterinary practice, breed society or feed company, and it does not sell animals, supplements or breeding services. Every page compiles published reproduction data into calculators, charts and guides, and the sources behind each figure are listed on the species pages.
Corrections matter more to us than anything else. If you spot a figure that disagrees with a reliable reference, or a breed that is missing, email animalgestation@gmail.com or use the contact page and we will check it against the sources and update the page. Every species page shows the date it was last updated.
Where the numbers come from
Every average on the site is taken from established livestock and veterinary reference data rather than anecdote. Cattle gestation figures follow Beef Improvement Federation breed standards. Equine figures follow published equine reproduction literature and American Association of Equine Practitioners guidance. Canine and feline figures follow theriogenology references, which is why the canine calculator distinguishes the ovulation date from the mating date.
For every species we record three numbers: the average gestation length, and the shortest and longest lengths considered normal. Where sources disagree we use the figure reported by the larger or more recent study, and we prefer data from working herds and veterinary case series over single-animal reports. The main references are the Merck Veterinary Manual, university agricultural extension services such as Penn State Extension, breed societies and registries, and, for wild species, zoo husbandry manuals and published zoological studies of captive births.
Breed averages come from breed association data where it exists. Each species period page ends with a Sources section naming the references used for that animal, so you can check any figure yourself.
How the estimates are calculated
The calculator adds the selected gestation length to the breeding date. Where breed data exists, choosing the breed changes the number of days used. For cattle, calf sex shifts the estimate by a day in either direction. The earliest and latest dates come from the published normal range for that species, or from a fixed tolerance where the counting method itself is the main source of error, as with a canine mating date.
What it is not
It is not a diagnostic tool and it is not veterinary advice. Averages describe populations, not the animal in front of you. Confirm pregnancy with your vet, prepare the birthing area before the earliest date in the range, and call for help early if labour does not progress normally.
Species covered
- cow gestation period guide — 283 days average
- horse gestation period guide — 340 days average
- dog gestation period guide — 63 days average
- cat gestation period guide — 64 days average
- rabbit gestation period guide — 31 days average
- sheep gestation period guide — 147 days average
- goat gestation period guide — 150 days average
- pig gestation period guide — 114 days average
- donkey gestation period guide — 365 days average
- alpaca gestation period guide — 345 days average
- llama gestation period guide — 350 days average
- camel gestation period guide — 395 days average
- water buffalo gestation period guide — 310 days average
- guinea pig gestation period guide — 68 days average
- hamster gestation period guide — 16 days average
- ferret gestation period guide — 42 days average
- rat gestation period guide — 22 days average
- mouse gestation period guide — 20 days average
- gerbil gestation period guide — 25 days average
- chinchilla gestation period guide — 111 days average
- african elephant gestation period guide — 645 days average
- asian elephant gestation period guide — 617 days average
- giraffe gestation period guide — 430 days average
- lion gestation period guide — 110 days average
- tiger gestation period guide — 105 days average
- white rhinoceros gestation period guide — 490 days average
- hippopotamus gestation period guide — 240 days average
- sperm whale gestation period — 530 days average
- blue whale gestation period — 340 days average
- dolphin gestation period guide — 365 days average
- walrus gestation period guide — 460 days average
- manatee gestation period guide — 380 days average
- grizzly bear gestation period guide — 235 days average
- gorilla gestation period guide — 257 days average
- chimpanzee gestation period guide — 237 days average
- red kangaroo gestation period guide — 33 days average
- virginia opossum gestation period guide — 13 days average
- red fox gestation period guide — 52 days average
- grey squirrel gestation period guide — 44 days average
- white-tailed deer gestation period guide — 200 days average
- zebra gestation period guide — 375 days average
- human — 280 days average
Suggestions for species to add are welcome through the contact page.
Follow the project
New species pages, breeding calendars and calculator improvements are announced on our social channels. Follow along, share a due date, or tag us with a question.