Swine Gestation Calculator

How to use the Swine Gestation Calculator#

1. Enter the breeding date. Use the date of mating, or of insemination.
2. Check the length. Leave the average, or enter your vet’s figure for the breed.
3. Read your dates. You get the expected date, the likely window and your sow’s progress.

How long is a sow pregnant?#

The average is 114 days, with most sows farrowing between about 111 and 117 days. A sow with a very large litter may farrow slightly earlier.

Getting ready for the piglets#

Move the sow to a clean farrowing pen about a week before the due date, and let her settle. In the final days she may become restless and start nesting, and her udder will fill. A farrowing crate can protect piglets from being crushed. Keep the pen warm for the piglets, with a heat lamp or mat in a corner.

If a sow hasn’t returned to heat about three weeks after breeding, she is likely to be pregnant, and a vet can confirm it by ultrasound. Call a vet if farrowing stalls.

Why the date is a window#

Sows farrow inside a short window: most between day 111 and 117, with 114 as the average. A very large litter can bring it forward a little. Because the window is so tight, most herds move the sow to the farrowing pen about a week before the due date rather than waiting for the exact day. This calculator is a planning tool and doesn’t replace veterinary advice.

A worked example#

A sow is served on Mon 11 January 2027. At 114 days she is due to farrow on Wed 5 May 2027, with a window from Sun 2 May 2027 to Sat 8 May 2027. Halfway is Tue 9 March 2027, and the final stretch begins on Sun 18 April 2027 (day 97).

Pig keepers remember the length as three months, three weeks and three days. It is close enough to 114 to work in your head, and the calculator does the exact count.

Confirming she is in pig#

The first sign is that she does not come back into heat. A sow normally returns to oestrus 18 to 24 days after an unsuccessful service, so a quiet sow on Thu 4 February 2027 is a good sign. Ultrasound scanning from about three to four weeks gives a firm answer, and it is worth doing on every sow, because carrying an empty sow for months costs a great deal in feed.

Write the service date on the sow’s record the same day. Many farms also keep a farrowing wheel or chart, and this calculator can replace it.

Moving to the farrowing pen#

Move the sow to her farrowing pen about five to seven days before the earliest date in the window, so she has time to settle, which is around Sun 25 April 2027 here. Clean and disinfect the pen beforehand, and let it dry. A sow often starts building a nest 12 to 24 hours before she farrows, so watch for restlessness, a swollen vulva and milk in the teats.

Farrowing normally takes between two and six hours, with piglets arriving every 15 to 20 minutes or so. If she has been straining for more than an hour with no piglet, or there are long pauses while she is clearly still in labour, call the vet.

Newborn piglets cannot hold their body heat, so provide a warm creep area, typically around 30 to 35 °C for the first days, and make sure each piglet gets colostrum in the first hours. She will return to heat three to seven days after weaning.

Keeping farrowing records#

Note the service date, the boar or the semen batch, the farrowing date and the number of piglets born alive, stillborn and weaned. A sow that regularly farrows on day 112 or 116 can have that figure entered in the length box. The same record helps you decide which sows to keep, since litter size and survival are what pay the bills.

A note on induced farrowing#

Some farms use hormones to bring farrowing forward to a working day. That is a veterinary decision, and it only works when the sow has gone far enough into the window. The calculator gives you the planning date, not the day on which it is safe to intervene.

Last reviewed October 2026 by the Calclulo team.