Polar Bear Gestation Calculator
This polar bear gestation calculator finds the expected birth date instantly. Enter the mating date to calculate the gestation window, view key milestones, and learn about denning behavior and delayed implantation.
Quick Answer
Polar bear pregnancy spans 195–265 days due to delayed implantation — actual embryo development is only 60–70 days. Litters average 1–3 cubs. Enter your mating date above for an estimated birth window.
Polar Bear Gestation Calculator
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Delayed Implantation Explained
After mating in spring, the fertilized egg does not implant in the uterine wall right away — it floats freely in a dormant state for months. Implantation only occurs in autumn, and only if the female has accumulated enough fat reserves from summer hunting. If she has not gained sufficient fat, her body reabsorbs the embryo entirely and the pregnancy simply ends without ever fully beginning. This remarkable reproductive strategy ties reproduction directly to a female's physical condition, ensuring cubs are only born when the mother can realistically support them through the brutal Arctic winter.
Denning Behavior
Pregnant females dig snow dens, typically in October or November, and give birth in December or January while still inside the den. The mother and newborn cubs remain denned through the depths of winter, emerging together in March or April once the cubs are strong enough to survive the Arctic cold outside. Cubs are born astonishingly tiny — around 500 grams, roughly 1/100th of their mother's weight — reflecting how much of a cub's growth happens after birth rather than in the womb.
Eight Months Without Eating
A pregnant female polar bear does not eat at all for roughly 8 months, from entering her den in October through emerging with cubs in March or April. She survives entirely on stored body fat while also producing rich milk to nurse her cubs, making pre-denning fat accumulation absolutely critical to both her survival and theirs.
Climate Change Impact on Reproduction
Sea ice loss is shortening polar bears' hunting season, since they rely on sea ice to hunt seals, their primary prey. Females are increasingly arriving at denning sites too thin to sustain a pregnancy through the winter fast, leading to lower cub survival rates and, in some populations, declining birth rates — one of the clearest documented links between climate change and a specific species' reproductive success.
How Polar Bear Gestation Compares to Other Bears
| Species | Avg. Days | Notes |
|---|---|---|
| Polar Bear | 195–265 days | Delayed implantation |
| Brown Bear | 180–270 days | Delayed implantation |
| Black Bear | ~220 days | Delayed implantation |
| Grizzly Bear | ~220 days | Delayed implantation |
See our brown bear gestation calculator and all bear species calculator.
How We Calculate Polar Bear Gestation
The calculator uses the formula: Birth Date = Mating Date + 240 days (average, accounting for delayed implantation). The estimate is derived from published wildlife biology and zoo husbandry research.
Frequently Asked Questions
Sources & References
- IUCN Red List — Polar bear conservation status
- Merck Veterinary Manual — Ursid reproduction
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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 4, 2026