Swine Gestation Calculator
Enter the date your sow was bred and the expected gestation length to get the estimated farrowing date, the earliest and latest plausible delivery window, and a count of days remaining until delivery. Switch to reverse mode to work out when breeding must have occurred from a known or expected farrowing date. Key management milestones appear in a schedule below so you can plan ultrasound checks, pen moves, and farrowing preparations in advance.
How to use the swine gestation calculator
Select "Breeding date to farrowing date" (forward mode) and enter the date the sow was bred or inseminated. Choose the gestation length that best matches your breed and herd history - the default of 114 days is accurate for most commercial breeds. The calculator instantly shows the estimated farrowing date, the earliest and latest dates within the normal window, and a countdown of days remaining. Switch to reverse mode if you know when farrowing is expected and want to estimate the breeding date.
Swine gestation: the "3-3-3" rule
Pig producers commonly remember the gestation period as "3 months, 3 weeks, and 3 days," which equals 114 days. This is the average for most commercial breeds including Yorkshire, Landrace, Duroc, Hampshire, and Berkshire. The normal range extends from about 112 to 120 days. Births before day 109 are classified as abortions or premature farrowings and require immediate veterinary attention. If a sow reaches day 120 without farrowing, veterinary assessment is necessary to rule out uterine inertia or fetal positioning problems.
Key management milestones during gestation
Effective swine production depends on acting at the right points during the 114-day gestation. At day 21, check whether the sow has returned to heat - failure to return strongly suggests successful conception. At day 30, ultrasound pregnancy confirmation is reliable and can estimate litter size. Between days 60 and 90, the fetuses grow rapidly and the sow's energy requirements increase significantly. By day 90, the sow should be moved to the cleaned and disinfected farrowing pen so she can settle before delivery. From day 110, monitor closely for pre-farrowing signs: nest-building behavior, vulval swelling, milk "letdown" (colostrum expression), and restlessness.
Farrowing preparation checklist
About one week before the expected farrowing date: clean and disinfect the farrowing crate or pen, set up the piglet heat lamp to maintain a zone of 32-35 C (90-95 F) at piglet level while keeping the sow comfortable at 18-22 C (64-72 F), check that the creep area is accessible, stock clean towels, iodine solution for navel dipping, colostrum supplement in case a piglet cannot nurse, and a record sheet for births. During farrowing, piglets are typically delivered at intervals of 10-30 minutes. Assistance may be needed if intervals exceed 45-60 minutes or signs of distress are present. Ensure each piglet nurses within the first hour to receive colostrum.
Swine reproductive reference values
| Parameter | Typical value | Notes |
|---|---|---|
| Gestation length | 112-120 days | Average 114 days (3 months, 3 weeks, 3 days) |
| Estrous cycle | 18-24 days | Averages about 21 days |
| Duration of estrus (heat) | 2-3 days | Optimal breeding on day 1-2 of standing heat |
| Age at sexual maturity | 5-7 months | Gilts should not be bred at first heat |
| Recommended first breeding age | 7-8 months | At least 230 days old and 130+ kg body weight |
| Average litter size (commercial) | 10-14 piglets born | Fourth and later parities typically largest |
| Farrowing interval | 155-165 days | Gestation + lactation (3-4 weeks) + weaning interval |
| Pre-term threshold | Before day 109 | Births before day 109 classified as abortion/premature |
| Overdue threshold | After day 120 | Veterinary assessment recommended if not farrowed by day 120 |
Standard values for domestic pig (Sus scrofa domesticus). Individual animals and herds may vary.
Frequently asked questions
How long is a pig's gestation period?
The average gestation period for domestic pigs is 114 days, commonly remembered as "3 months, 3 weeks, and 3 days." The normal range runs from about 112 to 120 days. Births before day 109 are considered premature or abortions and need veterinary attention. If a sow passes day 120 without farrowing, consult a veterinarian.
How many piglets does a sow have per litter?
Commercial sows typically give birth to 10-14 live piglets per litter, though the range can be 1 to 20 or more. Litter size generally increases with parity (number of pregnancies): gilts (first-time mothers) average fewer piglets than sows on their fourth or fifth litter, which tend to be the largest. Modern high-prolific breeds such as Large White and Landrace have been selected for litter sizes exceeding 14 piglets born alive.
At what age can a gilt (young female pig) be bred?
Gilts reach puberty at 5-7 months of age, but most producers do not breed them at the first heat to allow for additional physical development. The recommended approach is to breed at the second or third heat, when the gilt is at least 7-8 months old and weighs at least 130 kg (about 290 lb). Breeding too early results in smaller litters and can compromise the gilt's long-term productivity.
What are the signs a sow is about to farrow?
The main pre-farrowing signs appear within 12-24 hours before delivery: the sow becomes restless and builds a nest if given bedding material, her vulva swells and reddens, the mammary glands fill and colostrum can be expressed from the teats, and her body temperature may drop slightly (around 0.5 C below her normal 38.5-39.5 C). Mucous discharge from the vulva and visible contractions signal that farrowing has begun.
Can gestation length vary by pig breed?
Yes, but the variation among common domestic breeds is small - typically within the 112-116 day range. Heritage and crossbred animals, and some Asian breeds such as Meishan, may show slightly different averages. Miniature breeds (potbelly pigs, Kunekune) generally follow the same 112-120 day range as commercial breeds. Environmental stress, nutritional deficiency, and high ambient temperature can shorten gestation slightly.
What does the farrowing date calculator account for?
This calculator adds the selected gestation length (112-116 days) to the breeding date to give the estimated farrowing date. It also calculates the earliest normal farrowing date (day 109), the latest normal date (day 120), a days-remaining countdown from today, and a schedule of key management events. It does not account for breed-specific sub-day variation or individual sow history, so treat results as planning estimates rather than exact predictions.
How often can a sow farrow per year?
With a 114-day gestation and a 21-28 day lactation period followed by a short weaning-to-estrus interval of 4-7 days, a commercial sow can achieve about 2.2-2.4 litters per year. The farrowing interval (time from one farrowing to the next) is typically 155-165 days under commercial management. Longer lactation periods reduce the number of litters possible per year.