Bison Gestation Calculator
This bison gestation calculator finds the expected calving date instantly. Enter the breeding date to calculate the gestation period, view key milestones, and plan for calving season.
Quick Answer
The gestation period for a bison averages 277 days (about 9.1 months), with a normal range of 270–285 days. Enter the breeding date above to calculate the exact expected calving date.
Bison Gestation Calculator
Free tool — no signup required
How Long Are Bison Pregnant?
Bison are pregnant for 277 days on average. First trimester: embryo implantation and organ development, mirroring the pattern seen in domestic cattle. Second trimester: steady fetal growth, typically the most stable phase. Third trimester: rapid fetal weight gain, with the calf gaining the majority of its birth weight in the final months.
Calving Season, Litter Size & Signs
Bison calving season peaks April through May in North America, timed to align with spring grass growth. Bison almost always produce a single calf — twin pregnancies are rare and high-risk, as in cattle.
Signs a bison cow is close to calving mirror cattle: udder filling, relaxed pelvic ligaments, vulva swelling, and separation from the herd in the final hours.
Gestation by Bison Type
| Type | Avg. Gestation (Days) |
|---|---|
| American Plains Bison | 277 days |
| Wood Bison | 283 days |
How Bison Compare to Cattle
| Animal | Avg. Gestation (Days) | Vs. Bison |
|---|---|---|
| Horse | 340 days | 63 days longer |
| Cattle | 283 days | 6 days longer |
| Bison | 277 days | — |
| Goat | 150 days | 127 days shorter |
See our cattle gestation calculator for general cattle content.
How We Calculate Bison Gestation
The bison gestation calculator uses the formula: Calving Date = Breeding Date + 277 days. The average is derived from published wildlife and livestock research.
Frequently Asked Questions
Sources & References
- USDA — Bison production data
- Merck Veterinary Manual — Bovid reproduction
Related Calculators
Cattle & Cow Gestation Calculator
283 days avg
Goat Gestation Calculator
150 days avg
Dog Gestation Calculator
63 days avg
Pig Gestation Calculator
114 days avg
Rabbit Gestation Calculator
31 days avg
Sheep Gestation Calculator
147 days avg
Horse Gestation Calculator
336 days avg
Llama Gestation Calculator
350 days avg
Donkey Gestation Calculator
365 days avg
Cat Gestation Calculator
65 days avg
Deer Gestation Calculator
201 days avg
Elephant Gestation Calculator
645 days avg
Giraffe Gestation Calculator
457 days avg
Mare Gestation Calculator
340 days avg
Mice Gestation Calculator
20 days avg
Guinea Pig Gestation Calculator
65 days avg
Hamster Gestation Calculator
16 days avg
Alpaca Gestation Calculator
340 days avg
Ferret Gestation Calculator
42 days avg
Beef Cattle Gestation Calculator
283 days avg
Chicken (Egg Incubation) Gestation Calculator
21 days avg
Duck (Egg Incubation) Gestation Calculator
28 days avg
Dog (Whelping) Gestation Calculator
63 days avg
Pig (Farrowing) Gestation Calculator
114 days avg
Goat (Kidding) Gestation Calculator
150 days avg
Goose (Egg Incubation) Gestation Calculator
30 days avg
Turkey (Egg Incubation) Gestation Calculator
28 days avg
Quail (Egg Incubation) Gestation Calculator
17 days avg
Sheep (Lambing) Gestation Calculator
147 days avg
Horse (Foaling) Gestation Calculator
340 days avg
Cattle (Calving) Gestation Calculator
283 days avg
Rabbit (Kindling) Gestation Calculator
31 days avg
Chinchilla Gestation Calculator
111 days avg
Rat Gestation Calculator
22 days avg
Gerbil Gestation Calculator
25 days avg
Hedgehog Gestation Calculator
35 days avg
Camel Gestation Calculator
400 days avg
Zebra Gestation Calculator
375 days avg
Wolf Gestation Calculator
63 days avg
Dairy Cattle Gestation Calculator
279 days avg
All Gestation Periods
Complete comparison chart
GestationCalc Editorial Team
Our editorial team includes animal husbandry specialists, veterinary consultants, and agricultural extension educators. Content is reviewed against peer-reviewed research and guidance from USDA, Penn State Extension, and the Merck Veterinary Manual.
Last reviewed: September 1, 2026