Cattle gestation is remarkably consistent: about 283 days, nine months and a week, with most calves arriving within a week either side. Knowing the date matters for drying off dairy cows, timing vaccines that protect the calf through colostrum, and being present at calving. This calculator gives the due date and the management checkpoints counted back from it.
How it is calculated
- Calving date = breeding or AI date + 283 days by default. Breed averages differ: Holstein and Jersey about 279–280, Angus 283, Charolais and Brown Swiss 288–292. Enter the figure for your breed or your herd’s records.
- Normal range is about 279 to 292 days. Calves born before 270 days are premature.
- Bull calves are carried one to two days longer than heifers; twins come a week early on average.
Example
A cow inseminated on May 10 has an average calving date of February 17, normal window February 13 to 26. Pregnancy can be confirmed by ultrasound from June 9 (day 30). For a dairy cow, dry-off is around December 18 (60 days before), scours vaccines around December 22 and January 19 (8 and 4 weeks before), and she should be in the calving pen from about January 31.
Signs calving is close
The udder fills over the last two weeks and becomes tight in the final day or two; the vulva swells and the ligaments either side of the tail-head sink so the pin bones look prominent; the cow separates from the herd, is restless and may hold her tail out. Stage one labour (contractions, water bag) takes 2–6 hours in cows, longer in heifers; once the calf’s feet appear, delivery should be complete within an hour or two.
Frequently asked questions
How long is a cow pregnant?
About 283 days, just over nine months, with a normal range of roughly 279 to 292 depending on breed and the calf’s sex.
When can I check if a cow is pregnant?
Ultrasound from about day 28–30; rectal palpation by a vet from about day 35–45; blood tests for pregnancy proteins (PAGs) from day 28. Non-return to heat at 21 days is an early hint, not a confirmation.
How long is the dry period before calving?
For dairy cows, 45–60 days. Stop milking about two months before the due date so the udder can rebuild for the next lactation.
What is the gestation length for different breeds?
Holstein 279, Jersey 280, Hereford 285, Angus 283, Simmental 289, Charolais 289, Brown Swiss 290. Use the breed figure in the calculator for a more accurate date.
How long should calving take?
Once the water bag appears, a cow should deliver within 1–2 hours and a heifer within 2–3. Call for help if there is no progress after 30 minutes of hard straining, or if only one leg or the head is showing.
Sources
- Merck Veterinary Manual: Gestation periods of domestic animals
- Penn State Extension: Calving management
By Calcelate Team. Formula from the sources above.
- 2026-09-14 · Formula and texts checked