Calving calculator and cow gestation chart
Cows are pregnant for about 283 days, a little over nine months, and the bull's breed can move that by more than a week.
Put in the day she was served, or the day the bull went in, and see when she's due to calve. Pick the bull's breed and the calculator uses the right pregnancy length. It works backwards too, if you know when you want her to calve. Further down there's a gestation chart covering a year of service dates that you can print and pin up.
Add it to see when the last calves are due.
The calf's breeding sets the length, so go by the bull.
Semen catalogues often give a figure for each bull.
Pick the date she was served or the bull went in.
This calculator does one cow at a time
Agrianta works out expected calving dates for the whole herd from each service record and the bull's breed.
- Services recorded where they happen
- Bull, straw, technician and date, entered at the crush or in the field, even without signal.
- A calvings-due list
- Every cow due in the coming weeks, worked out from her service and the breed's pregnancy length.
- Fertility from the same records
- Calving intervals, services per conception and repeat breeders, without another sum.
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Cow gestation chart for services from November 2026
Calving dates for a service on the 1st or 15th of each month, using the 283-day average. Most cows calve within six days either side of the date. Calves by some breeds of bull come sooner or later, so check the table under the chart.
| Served | Calving due |
|---|---|
| 1 Nov 2026 | 11 Aug 2027 |
| 15 Nov 2026 | 25 Aug 2027 |
| 1 Dec 2026 | 10 Sep 2027 |
| 15 Dec 2026 | 24 Sep 2027 |
| 1 Jan 2027 | 11 Oct 2027 |
| 15 Jan 2027 | 25 Oct 2027 |
| 1 Feb 2027 | 11 Nov 2027 |
| 15 Feb 2027 | 25 Nov 2027 |
| 1 Mar 2027 | 9 Dec 2027 |
| 15 Mar 2027 | 23 Dec 2027 |
| 1 Apr 2027 | 9 Jan 2028 |
| 15 Apr 2027 | 23 Jan 2028 |
| 1 May 2027 | 8 Feb 2028 |
| 15 May 2027 | 22 Feb 2028 |
| 1 Jun 2027 | 10 Mar 2028 |
| 15 Jun 2027 | 24 Mar 2028 |
| 1 Jul 2027 | 9 Apr 2028 |
| 15 Jul 2027 | 23 Apr 2028 |
| 1 Aug 2027 | 10 May 2028 |
| 15 Aug 2027 | 24 May 2028 |
| 1 Sep 2027 | 10 Jun 2028 |
| 15 Sep 2027 | 24 Jun 2028 |
| 1 Oct 2027 | 10 Jul 2028 |
| 15 Oct 2027 | 24 Jul 2028 |
Adjusting for the bull's breed
| Bull's breed | Pregnancy length | Against the chart |
|---|---|---|
| Holstein Friesian | 279 days | 4 days sooner |
| Aberdeen Angus | 283 days | Same |
| Blonde d'Aquitaine | 294 days | 11 days later |
Agrianta works out the calving date for every cow from her service record and the bull's breed. Start your free trial
How the dates are worked out
- Cows carry a calf for about 283 days on average. Breed moves it: in Ireland's national figures, Holstein Friesians average 279 days and Blonde d'Aquitaine 294, more than two weeks apart.
- Go by the bull. In a study of 9,750 dairy cow pregnancies, calves by Limousin bulls ran about five and a half days longer than calves by Holstein Friesian bulls. AHDB publishes a gestation figure for dairy bulls for the same reason.
- Cows rarely calve on the day. In that study most calved within six days either side of the average, so the calculator shows that spread. Twins came about four days early.
- If the bull runs with the herd, the day he goes in gives the first calves and the day he comes out gives the last.
To see how tight your calving is year to year: Calving interval: how to calculate it.
Sources
Common questions
How long is a cow pregnant?
About 283 days, a little over nine months. It depends on the breed of the calf: in Ireland's national figures, Holstein Friesians average 279 days and Blonde d'Aquitaine 294.
How do I work out a cow's calving date?
Add the pregnancy length for the bull's breed to the service date. With the 283-day average, a cow served on 1 June is due on 11 March.
Do bull calves take longer?
Slightly. Bull calves usually arrive a day or two after heifers, and twins come a few days early.
When should I serve a cow to calve on a set date?
Take the pregnancy length off the date you want. To start calving on 1 March with the 283-day average, serve from 22 May.
Last updated 4 November 2026