Pig Gestation Calculator

How to Use This Calculator

Enter the date your sow was bred or artificially inseminated. Select the breed if known - though swine breeds have very similar gestation lengths, ranging from 113 to 115 days. Click Calculate Due Date to see the expected farrowing date and a full milestone timeline.

The calculator stores your last entry in the browser, making it easy to track multiple sows during peak breeding and farrowing seasons.

Pig Gestation Period - What to Expect

The gestation period for pigs is one of the most predictable in livestock at exactly 114 days (range: 112 to 116). The question of how long is a pig's gestation period is one of the easiest to remember in all of livestock production - it's exactly 3 months, 3 weeks, and 3 days. The consistency of the gestation period of pigs makes production scheduling highly reliable, which is one reason commercial pig farming operates on tight all-in/all-out cycles.

Days 1 to 30 (Early gestation): Embryos implant in the uterine horns around days 12 to 18. This is the most critical period - heat stress, mycotoxins, or nutritional deficiencies during early gestation can cause embryo loss. Feed gestation-specific rations and maintain comfortable temperatures.

Days 30 to 85 (Mid-gestation): Fetal development continues at a steady pace. Pregnancy can be confirmed by ultrasound at day 25 to 30 or by return-to-estrus check at day 18 to 24. Maintain sow body condition score (BCS 3 to 3.5) throughout this period.

Days 85 to 114 (Late gestation): Rapid fetal growth occurs, with 60 to 70% of final birth weight gained in the last 4 weeks. Increase feed intake in the final 2 weeks (flushing) to maximize colostrum and milk production. Move the sow to the farrowing house at day 107 to 110.

Research from Iowa State University Extension and USDA shows that farrowing rate and litter size are strongly influenced by gilt age at first service, BCS at breeding, and heat stress management - particularly critical in summer months.

Breed-Specific Pig Gestation Periods

The 3-3-3 Rule - Explained

The 3-3-3 rule is the classic mnemonic for pig gestation: 3 months + 3 weeks + 3 days = 114 days. It's one of the most memorable facts in all of livestock production. Here's the breakdown:

Signs of Pig Pregnancy

Confirming pregnancy early helps reduce open sow days and improve production efficiency. Here are the key signs and confirmation methods:

• →No return to estrus (days 18 to 24): The most common field check. A sow that does not show heat at her expected estrus window is presumed pregnant.
• →Ultrasound (days 25 to 35): Real-time ultrasound can detect fluid-filled uterine horns at day 25 and embryos at day 28 to 30. Most reliable confirmation method.
• →Belly enlargement (days 80+): Visible abdominal enlargement becomes apparent in the final month, especially in gilts with smaller litters.
• →Mammary development (day 100+): Udder begins to develop noticeably. Waxing of the teats typically occurs 12 to 24 hours before farrowing.
• →Nesting behavior (day 110 to 114): Sows often root bedding and show restlessness as farrowing approaches.

Farrowing Checklist

Move sows to the farrowing crate at day 107 to 110 (1 week before expected farrowing). Use this checklist to prepare:

The Sow's 114 Days Week by Week

Swine gestation is famously rigid: 114 days, give or take two, almost regardless of breed, litter size, or parity. That predictability is a gift. It means a farrowing date written the day of service is nearly as trustworthy as one written at day 100, and the whole production calendar can hang off it.

Week one begins at standing heat. The sow ovulates late in her standing heat, and the fertilized eggs take about three days to reach the uterus, then wander in the long uterine horns until around day 12. That wandering phase quietly decides litter size, because crowded or stressed embryos are lost here. By day 14 implantation is complete, and by day 18 to 24 comes the first real test: a settled sow never comes back into heat.

In weeks 4 through 9, days 22 to 63, embryos become fetuses. Organ formation finishes around day 35; by day 60 the fetus is fully formed and everything after is growth. Ultrasound between day 25 and 35 confirms the pregnancy and clears open sows for rebreeding, which makes it the single most profitable management hour of the whole 114 days.

Weeks 10 through 13, days 64 to 90, are quiet. Mammary tissue develops, skeletons harden, and the gestation ration does its job. The instinct here is to feed generously, but overfed sows farrow slower and lie on more piglets, so hold body condition steady rather than pushing it upward.

The final fortnight carries 60 to 70 percent of birth weight and all of the preparation. From day 105 the countdown turns physical: wash the sow, crate her, hang the heat lamp, and start twice-daily checks. Udder swelling two to three days out, waxy teats inside 24 hours, and the nest-building restlessness of day 111 to 113 tell you farrowing is hours away. If you are still working out whether a breeding took at all, the guide to telling if a pig is pregnant covers every confirmation option in order.

Farrowing Prep: Day 105 Onward

Day 105 is when a due date becomes a project. Well-run barns wash sows as they leave gestation housing, because a clean sow moving into a disinfected crate breaks the parasite and disease cycle right before piglets are born onto the floor. Scrub the crate itself, dry it, and run a hand over the bars looking for protruding bolts and broken welds, the two classic piglet injury sources. Move the sow in around day 107 to 110: early enough to settle, late enough that the crate does not stress her through the heavy growth phase.

Set the microclimate before she arrives. Newborn piglets need roughly 32 to 35 degrees Celsius at floor level in their creep area, delivered by heat lamp or mat, while the sow herself is comfortable far cooler, around 18 to 21. The lamp hangs over the creep, never over the sow. A well-set crate earns its keep here, because it lets piglets scatter to the heat and away from the sow instead of being crushed when she lies down.

Stock the farrowing kit at the same time: iodine for navels, dry towels, a bulb syringe for clearing airways, obstetric sleeves and lubricant, iron injection supplies for the day 3 shot, tooth clippers if your protocol uses them, colostrum or milk replacer for overflow piglets, and a record sheet that lives on the crate rail, not in the office.

From day 110, check twice daily and learn this sow's tells: udder swelling and firmness two to three days out, milky wax on the teats inside 24 hours, restlessness and pawing, then lying down with rhythmic straining. Farrowing usually runs 2 to 5 hours for the whole litter. Piglets arriving more than 45 minutes apart, or a sow straining hard with nothing produced, deserve a gloved internal check. The pig farrowing calculator projects each sow's dates automatically once service dates are entered, crate by crate.

Why Litter Size Varies

Two sows of the same age, in the same barn, on the same feed, will farrow nine and fifteen live piglets. Litter size is the most economically loaded number in swine production, and it varies for reasons worth understanding before you blame the feed.

Parity is the strongest pattern. Gilts breeding for their first litter produce smaller litters, commonly 8 to 10 piglets, because fewer eggs are released and the reproductive tract is still maturing. Litter size climbs through the early parities and typically peaks around the third to fifth, when a good sow drops 13 to 15. After the sixth or seventh parity, pig counts hold but birth weights and survival often slide, which is why most herds cull in that range.

Breed sets the ceiling. Maternal lines like Yorkshire and Landrace are selected specifically for prolificacy and routinely produce 12 to 14. Meishan-influenced genetics famously carry litters several piglets larger than Western breeds, at the cost of fat and slow growth. Terminal breeds like Duroc and Pietrain were never selected for maternal traits, and their daughters are not the ones farrowing the big litters anyway.

Nutrition and timing finish the job. Sows flushed with extra energy in the two weeks before service ovulate more eggs; sows heat-stressed in the first three weeks of gestation lose embryos and farrow smaller litters, which is exactly why summer farrowing rates dip. Service timing matters too, because one well-timed mating at standing heat outperforms a rushed one. None of these levers work without the calendar, though: every litter you want in February is conceived in late October, so litter size is won at breeding, measured at ultrasound, and only collected at farrowing. The pig pregnancy week-by-week guide matches each of these jobs to the week it belongs in.

Frequently Asked Questions

Sources & References

• USDA NASS - Hog and pig production statistics
• Penn State Extension - Swine reproduction and farrowing management
• University of Minnesota Extension - Swine gestation and production
• Merck Veterinary Manual - Porcine reproduction

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