Multiple SpeciesComparisons

Animal Gestation Periods Compared — Complete Reference Table

Published September 17, 2026 · 6 min read

Quick Answer

Gestation periods span from 15–18 days (hamster) to 640–680 days (African elephant). Dogs and cats both average ~63–65 days. Goats and sheep both average ~147–150 days. Horses average 340 days (~11 months). The complete comparison table below covers 21 common and notable species.

Gestation periods across the animal kingdom reflect evolutionary strategies, brain complexity, required developmental state at birth, and ecological pressures. The table below provides average gestation lengths for 21 species — from the shortest-gestating common mammals to the elephant's extraordinary 22-month pregnancy. Use the individual calculators for each species to get exact due dates.

Animal Gestation Periods — Complete Comparison Table

Animal	Avg. Gestation (Days)	Approx. Months	Notes
Mouse	19–21	~0.6–0.7	Shortest common mammal; highly variable by litter size
Hamster	15–18	~0.5	Syrian hamster: 16 days; Dwarf hamsters: 18–21 days
Rat	21–23	~0.7	Very similar to mouse; slightly longer
Rabbit	28–32	~1	Small breeds: 28–30 days; large breeds: 31–33 days
Guinea Pig	59–72	~2–2.4	Pups born with eyes open; longest gestation of common rodent pets
Cat	63–65	~2.1	Average 65 days; range 60–69 days
Dog	58–68	~2	Average 63 days from ovulation; varies by breed
Pig (Domestic)	111–120	~3.7	Average 114 days; mnemonic '3 months 3 weeks 3 days'
Goat	143–157	~5	Average 150 days; dairy breeds may run 147–153 days
Sheep	144–152	~5	Average 147 days; prolific breeds slightly shorter
Deer (Whitetail)	200–205	~6.7	Rut in November → fawning in late May/June
Cattle (Beef)	278–290	~9.4	Angus: 283 days; Brahman: ~292 days
Cattle (Dairy)	275–285	~9.2	Holstein: ~279 days; Jersey: ~278 days
Horse (Mare)	320–360	~11	Average 340 days; colt foals slightly longer than fillies
Donkey	340–380	~12	Slightly longer than horse gestation
Zebra	360–396	~12.5	Longest of the equids
Camel (Dromedary)	370–440	~13	Bactrian camel similar range
Giraffe	453–464	~15	Gives birth standing; calf falls ~5 ft at delivery
Rhinoceros	450–480	~15.5	White rhino: ~16 months; Black rhino: ~15 months
Asian Elephant	617–640	~20–21	Slightly shorter than African elephant
African Elephant	640–680	~22	Longest gestation of any land mammal

What Determines How Long an Animal Is Pregnant?

Body size is the single strongest predictor of gestation length across mammals — larger animals tend to have longer pregnancies because they produce larger offspring that require more time to develop. But body size is not the only factor:

Neurological complexity: Elephants and orcas have longer gestations than their body size alone would predict because their calves must be born with highly developed nervous systems. The elephant's 22-month gestation is driven primarily by the time required to develop the largest brain of any land animal.

Developmental state at birth (altricial vs. precocial):Animals born altricial — helpless, blind, deaf, and requiring intensive parental care — tend to have shorter gestations. Mice (19 days) produce blind, hairless pups. Animals born precocial — developmentally advanced and capable of limited independence — tend to have longer gestations. Horses (340 days) produce foals that can gallop within hours.

Reproductive strategy: Prey animals under intense predation pressure evolved two different strategies: short gestations with many offspring (mice, rabbits) or long gestations with fewer but more developed offspring (horses, giraffes). Both strategies can be successful but require different ecological conditions.

The Surprising Similarities

The gestation comparison table reveals some unexpected patterns:

Dogs and cats are almost identical: Despite their differences, dogs and cats are both pregnant for approximately 63–65 days. This reflects similar body sizes and similar developmental requirements for their newborns.
Goats and sheep are nearly the same: Goats at 150 days and sheep at 147 days have essentially the same gestation — both are small ruminants of similar size producing similarly developed offspring.
Cattle gestation closely matches human gestation: Holstein cows at 279 days are almost exactly aligned with the human average of 280 days. This has no functional significance — it's coincidental.
Horses are significantly longer than donkeys expect:Horses at 340 days vs. donkeys at 360+ days — despite being sister species. Hybrid mules (horse × donkey) have intermediate gestations of approximately 350 days.

Find Your Species Calculator

Use the individual species calculators to calculate exact expected due dates:

Sources & References

Merck Veterinary Manual — Species reproductive data
IUCN Red List — Wildlife species accounts
National Wildlife Federation — Wildlife reproductive facts

→ Longest Gestation Periods in the Animal Kingdom → Elephant Gestation Period → Deer Gestation Period by Species

Frequently Asked Questions

What animal has the shortest gestation period?

Among common mammals, hamsters have the shortest gestation at 15–18 days. The Virginia opossum (a marsupial) gestates for only 12–13 days, though most development continues in the pouch. Among true placental mammals, the hamster is the shortest-gestating common species, followed by mice (19–21 days) and rats (21–23 days).

How does dog gestation compare to cat gestation?

Dog and cat gestation periods are remarkably similar. Dogs are pregnant for approximately 58–68 days (average 63 days from ovulation). Cats gestate for approximately 60–69 days (average 65 days). The similarity reflects similar body sizes and the comparable developmental state required in puppy and kitten newborns — both are born with eyes closed, limited mobility, and high parental dependency.

Why do larger animals have longer pregnancies?

The positive correlation between body size and gestation length across mammals reflects several factors: larger animals need larger, more developed offspring at birth; larger brains require more prenatal developmental time; and larger offspring take more time to grow to their birth size. However, the relationship isn't strict — elephants have longer gestations than their size alone would predict because of their exceptional brain complexity.

How long are goats and sheep pregnant compared to cattle?

Goats and sheep are both pregnant for approximately 5 months (147–150 days). Cattle are pregnant for approximately 9–9.5 months (280–283 days). Cattle gestation is roughly twice as long as goat and sheep gestation, reflecting cattle's larger body size and the heavier, more developed calves they produce at birth.

Which animals are pregnant for about the same time as humans?

Human gestation averages 280 days (40 weeks, ~9.2 months). Animals with similar gestations include: dairy cattle (Holstein: ~279 days), beef cattle (Angus: ~283 days), and some dolphin species (bottlenose dolphin: ~12 months). Gorillas and chimpanzees also have gestations similar to humans at approximately 250–280 days, which makes sense given their genetic proximity to Homo sapiens.

Do all dog breeds have the same gestation length?

Dog gestation length doesn't vary significantly between breeds — the average of 63 days from ovulation applies across toy, medium, and giant breeds. What does vary is litter size: Chihuahuas typically have 1–3 puppies per litter while Great Danes may have 8–12. The gestational hormonal and developmental biology is consistent across the species even as body size varies by a factor of 30 or more between smallest and largest breeds.

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Kanika

Researched and reviewed by Kanika, founder of GestationCalc. All gestation data is verified against primary veterinary and agricultural sources before publication.

Last reviewed: September 17, 2026

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