Pig Gestation Calculator NZ
This works out when a sow is due to farrow from the date she was mated or served. Pigs carry for about 114 days, which generations of pig keepers have remembered as three months, three weeks and three days, and the striking thing about pig gestation is how consistent it is. Most sows farrow between 112 and 116 days, a spread of four days in total, where a cow can easily be a week either side of her date and a mare a month. That consistency is what makes batch farrowing practical: a group of sows served in the same week will nearly all farrow in the same week, so the farrowing house can be filled, emptied and cleaned on a predictable cycle rather than trickling through. Litter size nudges the date a little, with bigger litters tending to arrive slightly early and small ones running on a day or two, and breed and age contribute small differences too. None of it moves the date far. The window shown here is two days either side rather than the week used for cattle, because that is what the species actually does, and using a wider window would suggest an uncertainty that is not there.
Estimate only, and a planning tool rather than veterinary advice. Talk to your vet about anything unusual before or during farrowing, and about the health programme leading into it.
How it works
The calculator adds the gestation length to the service date and marks a window two days either side. That window is not a rule of thumb borrowed from another species: it is what the published range for pigs actually is, with most sows farrowing between 112 and 116 days. The gestation length is editable, so if your own records show your herd running consistently at 115 days you can use that instead of the average and the window moves with it.
Worked example
A sow served on 1 August 2026 and carrying the average 114 days is due to farrow on 23 November 2026, with a likely window from 21 to 25 November. Moving her into the farrowing pen about a week before that date, on roughly 16 November, gives her time to settle before nesting begins. Because the window is only four days wide, a batch of sows served across that same first week of August will farrow across the same short window in November, which is exactly what a batch system depends on.
Related calculators
- Cow Gestation: calving due dates.
- Sheep Gestation: lambing due dates.
- Goat Gestation: kidding due dates.
- Mating Ratio: how many males a mating group needs.