Knowing when a cow is due is the backbone of dairy planning — it tells you when to dry her off, when to move her to the calving area, and when to watch for trouble. The good news: cow gestation is remarkably consistent, so the maths is easy.
The headline number A dairy cow's gestation averages about 283 days — call it roughly 9 months and 1 week from service to calving. It's consistent enough that a recorded breeding date gives you a reliable due date.
What shifts it (a little) - Breed: Holsteins average ~278–280 days; Jerseys and many other breeds run slightly longer (~283– 287). Brown Swiss are longer still. Know your breed's typical figure. - Calf sex: bull calves are carried a day or two longer than heifer calves, on average. - Twins: usually born a few days early. - Individual variation: a few days either side of the average is completely normal.
How to calculate the due date - Quick method: add 9 months and ~1 week to the service date. Bred on 1 March → due around 8 December. - Precise method: add your breed's exact gestation length (e.g. 280 days) to the confirmed service date. - Let the platform do it: this is exactly what recording a service in Vache is for — log the breeding date and the calving date is forecast automatically, along with the dry-off date that works back from it.
Why the due date drives two other key dates - Dry-off: cows are typically dried off about 60 days before calving to rest the udder and grow the calf — so the due date sets the dry-off date. Miss it and you shorten the dry period, which costs next lactation's milk. (See "How to dry off a dairy cow.") - Close-up move: shift her to the calving group ~3 weeks before, for transition management and to calve somewhere clean.
Confirm she's actually pregnant A due date only matters if she's in calf. Pregnancy-check (vet palpation, ultrasound, or milk/blood pregnancy test) from ~30–35 days after service so open cows get re-bred quickly instead of sitting empty on a phantom due date.
Sources Penn State Extension — Gestation and Calving Date Calculation. AHDB Dairy — Dry Period Management. ICAR — Gestation Length by Breed.