Gestation Calculator

Pig gestation calculator

A sow farrows about 115 days after breeding. The old rule of three months, three weeks and three days gives 114, which is now a day short of what herds actually do.

115 days

Put in the date she was bred and you will get the due date, the normal window either side of it, and the dates worth writing on the calendar between now and then. The full chart is further down the page.

How far apart the breeds really are

Every dot is a breed average. The shaded band is the normal window for a single pig — which is narrower than the gap between the shortest and longest breed, and that is the part worth noticing.

Traditional "3 months, 3 weeks, 3 days" 114average 115DanBred / high-prolificacy Danish 118

Gestation length by breed

Every figure below traces to a published study, and the ones we could not source are left out rather than guessed at. Pick a breed in the calculator and both the date and the window move with it.

BreedAverage gestationvs. pig averageNotes
Traditional "3 months, 3 weeks, 3 days"114 days-1The old mnemonic. Modern herds run a day or two past it.
Modern commercial lines115 dayseven115.3 days across 66,254 farrowings.
DanBred / high-prolificacy Danish118 days+3117.6 days, but from a single 92-sow farm. Calibrate off your own records.

The detail, if you want it

The three-three-three rule has drifted

Sasaki and Koketsu went through 66,254 farrowings and found the average sitting at 115.3 days. Only 19% of those sows farrowed on day 114, against 31% on day 115 and 22% on day 116. Merck now gives the range as 115 to 116 days rather than 114.

Litter sizes have climbed and the number crept up with them, and nobody went back to update the mnemonic. Herds running Danish high-prolificacy genetics report 117 or 118, though that comes from one farm of 92 sows, so treat it as a reason to check your own records rather than a number to adopt.

The consistency is still the good news. Where cattle spread over two weeks and horses over a month and a half, about 72% of sows farrow between days 113 and 117. A sow four days off her date is worth a second look.

Moving her at the right time

Sows go into the farrowing house or hut around day 110, which gives them three or four days to settle and to build a nest if they have the material for it. Move her later than that and you risk her farrowing where you did not want her to.

The calculator puts that move date on the timeline, because it is the one date that actually changes what you do on a given morning.

Gilts against sows, and what actually predicts her

You will read that older sows carry longer. Across those 66,254 farrowings the average held between 115.2 and 115.4 days at every parity, so there is nothing in it. Gilts still want more attention at farrowing — smaller litters, less colostrum, less patience — but not a different date on the calendar.

What does predict a sow is her own history. The same study put repeatability at 0.50, meaning a sow who went 117 last time is genuinely more likely to go long again. Her card beats any average on this page.

One number worth treating as a warning rather than a scheduling note: sows farrowing at 112 days or under had more dead piglets and were roughly twice as likely to be culled.

Full pig gestation chart

Every day of the year, bred to due — built to print

Find the breeding date in the left column of the right month, read across for the due date. Hit print and it comes out clean.

Bred in January
BredDue
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Bred in February
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Bred in March
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Bred in April
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Bred in May
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Bred in June
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Bred in July
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Bred in August
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Bred in September
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Bred in October
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Bred in November
BredDue
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Bred in December
BredDue
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Built on a 115-day gestation. Dates are month and day only, so this chart works for any year — with one catch: if the pregnancy runs through 29 February, the real due date lands one day later than the chart says. The calculator at the top of the page already accounts for that.

Questions people actually ask

How long are pigs pregnant?

About 115 days. The traditional answer is 114 — three months, three weeks and three days — but modern herds run a day longer than that, and Merck now gives the range as 115 to 116. Most sows farrow between 113 and 117 days.

What is the 3-3-3 rule for pigs?

Three months, three weeks and three days from breeding to farrowing, which counts out to 114 days. It is a good way to remember roughly when, and it is why nobody needs a calculator to get within a couple of days.

It is no longer the average, though. Across 66,254 farrowings only 19% happened on day 114, against 31% on day 115. Use the rule to remember, use the date above to plan.

When should a sow move to the farrowing pen?

Day 110, and treat that as a deadline rather than a suggestion. Crate, pen or hut, it gives her three or four days to settle and build a nest if she has anything to build one with, and it means she is not farrowing somewhere you did not choose.

How can you tell a sow is about to farrow?

Milk lets down 12 to 24 hours out — you can strip a teat and get a squirt. She gets restless, starts nesting, and her vulva swells and reddens. Once she lies on her side and settles into steady straining, piglets follow.

How soon can you preg check a sow?

Ultrasound from about 21 to 30 days is standard. Watching for a return to heat around day 21 is the free version and catches most of the failures.

Where these numbers come from

Every figure on this page traces to a university extension publication or a veterinary reference. If you think one is wrong, the sources are right here so you can check it yourself.

Worth knowing

  • 114 days is out of date. Merck states plainly that pig gestation "has been increasing and now ranges 115–116 ± 1 days." The largest commercial dataset we found — 66,254 farrowings — puts it at 115.3. Only 19% of those farrowings happened on day 114. We default to 115 and keep the three-three-three mnemonic for what it is: a good way to remember roughly when, not the modern average.
  • Gilts and old sows gestate the same length. That 66,254-farrowing dataset found no parity effect at all, which contradicts the common claim that older sows carry longer.
  • What does predict a sow is her own history. Repeatability is 0.50, so what she did last time is the best guide you have. Worth writing on the card.
  • Farrowing at 112 days or under is a warning, not just a scheduling problem. Those sows had more dead piglets and were roughly twice as likely to be culled.
  • We could not verify the claim that pot-bellied pigs carry 15 to 20 days longer. It appears to come from forum posts rather than data.

Figures last checked August 2026.

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