Pig Gestation Period: How Long Are Pigs Pregnant? Farrowing Date Chart and Calculator

The gestation period for pigs is about 114 days, the figure behind the old rule of “3 months, 3 weeks and 3 days”. Modern sows tend to carry a day or two longer: the Merck Veterinary Manual puts today’s average at 115 to 116 days from first service, and Penn State Extension says most sows farrow between days 110 and 117. If you know the breeding date, the free Creatures pig gestation calculator adds the 114 days for you and shows the window to be ready for, with no account needed.

So plan around day 114, and be ready a few days either side of it. The chart below gives the farrowing date for a breeding on the first of every month. The rest of this guide covers why sows vary, what happens during the pregnancy, how gilts and mini pigs compare, how to set up for farrowing, and when to call a veterinarian.

The 3 months, 3 weeks and 3 days rule

Every pig keeper learns the rule first because it is easy to remember and close enough to plan with. Three months is roughly 90 days, three weeks is 21 and three days is 3, so the rule lands on about 114 days. That is the number Purdue University’s College of Veterinary Medicine gives in its owner guide, What to Expect When Your Sow Is Expecting, the figure in Merck’s table of approximate gestation periods, and the average in University of Missouri Extension’s guide to care of pigs from farrowing to weaning.

The rule is a planning anchor, not a promise. The best large dataset we found is a study of 66,254 farrowings from 13,715 sows on 94 commercial farms, published in Theriogenology by Sasaki and Koketsu. Average gestation was 115.2 to 115.4 days across parities. About 19 percent of sows farrowed on day 114, 31 percent on day 115 and 22 percent on day 116, so roughly seven in ten landed inside that three-day stretch. The rest were spread either side of it. A 2022 review in the journal Animals, Defining “Normal” in Pig Parturition, gives the outer range across breeds and individuals as 105 to 125 days.

In practice: count 114 days to get the date to prepare for, expect the sow to farrow within a few days of it, and watch her closely from the week before.

Pig gestation chart: breeding date to farrowing date

This chart adds 114 days to a breeding on the first of each month. Use it as an estimate. Your sow may farrow a couple of days before or several days after the date shown.

A few notes on reading it:

• Leap years. If February 29 falls between the breeding and the due date, the due date is one day earlier than shown (a December 1 breeding before a leap-year February is due March 24, and a January 1 breeding in a leap year is due April 24).
• Other days of the month. Move the due date forward by the same number of days. A sow bred March 10 is due nine days after the March 1 date, on July 2.
• “Ready from” is two days early, which matches the start of the planning window the Creatures calculator shows (days 112 to 118). Penn State’s 110 to 117 range means a few sows go even earlier, so have the farrowing pen ready well before this date (see the setup section below).
• Several services. Many producers breed a sow once a day for as long as she stands for the boar, which Merck says often totals two or three inseminations. Count from the first service, which is how Merck states its average.

For any other date, the pig gestation calculator does the counting. Choose Exact Breeding Date for a single service, or Exposure Window if the sow ran with a boar over several days and you do not know the exact day. It returns the estimated farrowing date, the planning window, the signs that farrowing is near and a short pregnancy timeline. It is also the quickest answer to the “hog gestation calculator” question: the same 114-day count works for any domestic sow. The help center’s guide to using the gestation calculator walks through both modes, and there are gestation calculators for 18 other animals if you keep more than pigs.

Why one sow farrows early and another late

Her own history. In the Sasaki and Koketsu study, a sow’s gestation length in one litter was clearly related to her gestation length in her other litters, with a repeatability of 0.50. That is a strong case for writing the farrowing date down every time: a sow that farrowed on day 116 last time is more likely to do it again. The authors’ closing recommendation is that producers keep gestation length records for each parity of each sow.

Litter size. The evidence here is not tidy. Sasaki and Koketsu found shorter gestations went with more total piglets born. Penn State’s farrowing guide describes the opposite pattern in modern, highly prolific sows, where larger litters of smaller piglets can push farrowing out to 115 to 120 days, while smaller litters of larger piglets tend to come at 113 to 115 days. Either way, the takeaway is the same: litter size can shift the date by a few days, so do not treat day 114 as the start of your watch.

Gilts versus sows. A gilt is a young female before or during her first litter. Across parities in the large commercial study, average gestation moved by only a fraction of a day (115.2 to 115.4 days), so use the same 114-day count for a gilt. The differences that matter come before the pregnancy: Merck notes that estrus lasts about 36 to 48 hours in gilts and 48 to 72 hours or more in sows, so a gilt’s breeding window is shorter and her service dates are easier to miss. Write them down on the day.

Breed. We found no reliable source showing a practical difference in gestation length between the common US breeds, so plan every breed on the same count. Across the pig breeds on Creatures, breed matters more to litter size and mothering. The white maternal breeds, such as the Chester White and the Large White or Yorkshire, are kept for sow traits, while a terminal sire breed like the Hampshire is used to put muscle into market pigs. Our breed guides cover each one’s history, registry and what to ask a breeder.

Mini pigs and potbellied pigs. Merck gives potbellied pigs a gestation period of 113 to 115 days, essentially the same as farm sows, with litters of 1 to 12. Two things are different for pet pig owners. Potbellied females can reproduce as early as 3 months of age, which catches people out, and Merck advises spaying pet females at 4 to 6 months. And Purdue notes that potbellied sows have a higher rate of difficult births because of a narrower birth canal and heavier body condition, so line up your veterinarian before the due date. Our guides to the Juliana pig and the Yucatan miniature pig cover what “mini” really means for adult size.

Pig pregnancy week by week

Most of a pig pregnancy happens out of sight. Purdue notes that sows can show few signs until close to farrowing. These are the milestones that matter for planning, counted from the first service.

Days 0 to 30: establishing the pregnancy

Penn State’s guide to developmental milestones during pig gestation explains that embryos attach to the uterus around days 12 to 15, and that a sow needs at least four viable embryos for the pregnancy to continue. This is the stretch to keep her routine calm and steady.

The first check is simple: a sow that is not pregnant usually comes back into heat about three weeks after service. Merck lists daily heat checks from day 18 to 24 as 75 to 85 percent accurate for spotting open sows, and real-time ultrasound from day 27 onward as more than 95 percent accurate. Purdue tells owners a veterinarian can usually confirm pregnancy about 30 days after breeding. If she does come back into heat, record the new service date and the due date resets.

Days 30 to 90: steady growth

The piglets’ bones begin to calcify around days 35 to 45, per Penn State, and the placentas go through a final expansion from day 77. By day 90 the piglets are fully developed, and the last weeks are about growth and energy stores. From the outside you may see little until about days 80 to 90, when Purdue says a slight swelling of the belly can appear, followed by udder development.

This is the time to keep her in good, steady body condition and to plan preventive care. Purdue advises discussing vaccinations and deworming with your veterinarian before farrowing. Your veterinarian or feed supplier sets the actual feeding plan, because a sow that is too thin or too fat both bring problems at farrowing.

Days 90 to 114: getting ready

The last month is when the farrowing plan comes together. The next section covers setup. If you are raising a litter to sell, now is also a good time to think about pricing: our pig cost guide covers what feeder pigs, breeding stock and mini pigs sell for.

Getting ready for farrowing

Penn State notes that sows are commonly moved into farrowing pens or stalls up to 10 days before the predicted due date. Moving her early lets her settle before she farrows and gives you margin if she goes early.

A practical checklist, drawn from Purdue, Missouri and Penn State:

• Clean the pen first. Missouri Extension advises a thoroughly cleaned farrowing area, and washing the sow with soap and warm water just before she goes into the farrowing pen.
• Give her room and dry bedding. Clean, dry straw lets her nest, which is normal behavior in the last hours.
• Plan piglet warmth. Purdue says newborn piglets need an environment above 90°F for the first couple of weeks. If you use a heat lamp, put it in a protected corner where piglets can get under it but the sow cannot touch it, and keep every cord out of her reach.
• Protect piglets from crushing. Without a farrowing crate, Purdue notes, piglets are at greater risk of being lain on. A warm, protected corner gives them a safe place to rest between feeds.
• Assemble a farrowing kit. Purdue’s list includes clean dry towels, paper towels, an infant nasal bulb syringe, a thermometer, a heat source and a navel dip your veterinarian recommends.
• Write down a farrowing plan with your veterinarian, including when to call. Keep the number where everyone in the barn can see it. Our guide to finding a large animal vet helps if you do not have one yet; do it now, not on the night.

Signs of farrowing and when to call a veterinarian

Purdue’s owner guide describes the sequence. In the last week the vulva may swell and redden and the udder fills; colostrum can usually be expressed 24 to 48 hours before farrowing. In the final hours the sow becomes restless, builds a nest if she has bedding, urinates and defecates often and breathes faster. In the last 15 to 60 minutes she lies down on her side, contractions become visible and a little fluid may pass. Penn State adds that some of these changes appear only a couple of hours or minutes before the first piglet.

Once she starts straining, Purdue says the first piglet should arrive within 15 to 20 minutes, and the rest every 15 to 20 minutes after that (Penn State says about every 15 to 30). Piglets can come head first or back legs first, and placentas usually follow the last piglet.

Call for help when:

• She strains for more than 30 to 45 minutes without producing a piglet. Purdue says intervention is warranted at that point. Delivering piglets takes skilled hands, so if no one experienced is there, call your veterinarian immediately.
• She seems finished but something is not right. Merck notes that retained afterbirth is rare in pigs except when piglets remain in the uterus, which quickly becomes a medical problem needing a veterinarian.
• She is a potbellied pig, or has had a difficult farrowing before. Talk to your veterinarian ahead of time; Purdue flags potbellied sows as more prone to difficult births.
• She passes the end of the window with no signs. If she reaches the end of the calculator’s window (day 118) with no udder change or other signs, call your veterinarian to check her. Sasaki and Koketsu found that sows farrowing at 117 days or later had fewer piglets born alive than sows farrowing between 113 and 116 days.

Do not pull on a piglet yourself unless you have been shown how. After farrowing, make sure every piglet nurses early, because colostrum carries the antibodies that protect them until they can be vaccinated.

Tracking a sow’s pregnancy on Creatures

A farrowing has a lot of dates in it: each service, the heat check, the ultrasound, the move to the farrowing pen, the farrowing itself and then the litter’s own records. Creatures keeps them together on the sow’s profile, and it builds the gestation-length history that the large farm study recommends keeping for every sow.

Without an account. The pig gestation calculator is free for anyone and works for a single date or an exposure window. It is an estimate, and it does not save anything.

Record the breeding. Add the sow to Creatures, then choose Add record, Breeding & Reproduction, and turn on Track as breeding cycle. Enter the service method, the boar (a Creatures profile or just a name for an outside boar or AI sire) and the service date, or start and end dates if she ran with a boar. If your veterinarian gives you a due date from an ultrasound, use Projected date override instead of changing the service date. Step by step: recording a breeding.

Follow the pregnancy. Her Breeding tab shows the expected date and likely window, milestones and next actions. When better information comes in, adjust the projection and the open reminders move with it. See tracking pregnancy and progress, and set a reminder for the pen move ten days out with reminders and upcoming care.

See every sow due in one place. The breeding dashboard lists your active breedings in due-date order, grouped into Expecting, Due soon and Overdue. Overdue only means the window has passed without a recorded outcome, which is your prompt to check on her and call your veterinarian if she is past day 118. The dashboard helps you plan; it does not judge whether a pregnancy is healthy.

Record the farrowing and the litter. On the active cycle, record the birth with the date and the counts born alive and stillborn. Creatures closes the cycle, creates a private group for the litter, and lets you create piglet profiles linked to their dam now or later. See recording births and creating a litter. From there, the pig weight calculator estimates weight from a tape measure as the litter grows, and our livestock record keeping guide covers what else is worth writing down for a breeding herd.

Frequently asked questions

How long are pigs pregnant?

About 114 days, or 3 months, 3 weeks and 3 days. Modern commercial sows average a little longer, 115 to 116 days from first service according to Merck, and Penn State says most sows farrow between days 110 and 117.

How do I calculate a pig’s due date?

Add 114 days to the date of the first service. A sow bred March 1 is due June 23. The pig gestation calculator does it for any date and shows the window to be ready for.

Is the gestation period different for gilts and sows?

Not by enough to matter for planning. In a study of more than 66,000 farrowings, average gestation varied by less than half a day across parities. Gilts do have shorter heats than sows, so record their service dates carefully.

How long are mini pigs pregnant?

Merck gives 113 to 115 days for potbellied pigs, the same range you would plan for a farm sow. Potbellied females can breed from about 3 months old, and they are more prone to difficult births than farm sows, so involve your veterinarian early.

Can a sow farrow before 110 days?

It happens, but it is outside the range where most sows farrow. A 2022 review gives the outer range across breeds and individuals as 105 to 125 days. If a sow farrows well before day 110, or looks unwell at any stage, call your veterinarian.

How many piglets does a sow have?

It depends heavily on breed, age and management. Potbellied pigs have 1 to 12 per Merck, and commercial maternal lines are bred for large litters. Our breed guides, such as the Taihu pig and the Chester White, cover litter size by breed.

Do this next on Creatures

Whether you have just bred a sow, are planning your first litter, or are looking for breeding stock, these are the useful next steps.