How long are pigs pregnant?
The classic figure is 114 days [3][4][1], easy to remember as 3 months, 3 weeks and 3 days [4][5]. Normal farrowing runs from 113 to 117 days[5][2].
| Source | What it says |
|---|---|
| Missouri Extension [3] | Average 114 days |
| Purdue vet school [4] | 114 days: 3 months, 3 weeks and 3 days |
| Merck Vet Manual [2] | Average has been rising: now 115–116 ± 1 days from first service |
| NADIS (UK vets) [5] | Typically 115 days; 113–117 is normal |
Modern commercial sows tend to go a day or two longer. Merck notes that the average has been rising and now sits at 115–116 days from first service [2], and NADIS gives 115 as typical [5]. The calculator keeps 114 as the average, as Missouri and Purdue do, and shows the range to 117 so a later litter isn’t a surprise.
Farrowing dates for breeding on the 1st
Missouri Extension prints a table of breeding dates and farrowing dates at 114 days [3]. The calculator gives the same dates. When a February 29 falls during the pregnancy, the farrowing date is one day earlier.
| Bred on | Due to farrow |
|---|---|
| January 1 | April 25 |
| February 1 | May 26 |
| March 1 | June 23 |
| April 1 | July 24 |
| May 1 | August 23 |
| June 1 | September 23 |
| July 1 | October 23 |
| August 1 | November 23 |
| September 1 | December 24 |
| October 1 | January 23 |
| November 1 | February 23 |
| December 1 | March 25 |
Heat checks, scans and getting ready
| When | What |
|---|---|
| Day 18–24 | Watch for a return to heat. An open sow or gilt usually returns to heat 18–24 days after service. [2][6] |
| Day 26–30 | Ultrasound pregnancy check. Real-time ultrasound is generally used from about day 26–30. [2][4] |
| 5–7 days before the due date | Move into the farrowing area. Place her in the farrowing pen or crate 5–7 days before she is due. (per NADIS) [5] |
- Return to heat. A sow that didn’t settle usually comes back into heat 18–24 days after service[2][6]. Not every open sow shows it, so a missed return isn’t proof of pregnancy[2].
- Ultrasound is generally used from about day 26–30 [2]; Purdue says a vet can usually confirm pregnancy about 30 days after breeding [4].
- Late pregnancy. Some owners notice a slightly bigger belly from about day 80–90. In the last week the vulva may swell and redden, and the udder fills with colostrum 24–48 hours before farrowing[4]. NADIS advises moving the sow into the farrowing area 5–7 days before she is due[5].
Common questions
What is the 3-3-3 rule for pigs?
Pregnancy in pigs lasts about 3 months, 3 weeks and 3 days, which adds up to roughly 114 days[4][5]. Counting exact days is more reliable than counting months, because months differ in length; the calculator does that for you.
Is gestation the same for gilts and sows?
The sources here give one figure for gilts and sows, so the calculator uses the same range for both. Merck’s rising average is measured from first service [2].
Does this work for pot-bellied pigs?
Yes. Purdue’s 114-day guidance covers both domestic and pot-bellied sows [4].
What if she hasn’t farrowed by day 117?
She is past the published normal range. Recheck the service date, and talk to your vet if she is still waiting.
These dates are planning estimates from published averages, not veterinary advice. Your vet can confirm a pregnancy.
Sources
- Merck Veterinary Manual, table “Approximate Gestation Periods”Gestation by species; dog 62–64 days from ovulation, 58–72 days from breeding
- R. V. Knox, “Breeding Management of Pigs,” Merck Veterinary Manual (reviewed 2026)Average gestation now 115–116 ± 1 days; 18–24-day return to estrus; ultrasound at 26–30 days
- J. C. Rea, “Care of Pigs From Farrowing to Weaning,” MU Extension G2500Sow gestation averages 114 days; breeding-to-farrowing table
- J. H. Koziol, “What to Expect When: Your Sow is Expecting,” Purdue University VA-30-W114 days (3 months, 3 weeks, 3 days); pregnancy check about 30 days; late-pregnancy signs
- M. White, “Farrowing Process,” NADIS Pig Health BulletinTypically 115 days, 113–117 normal; farrowing area 5–7 days before
- BPEX “Action for Productivity” no. 29, “Effective Heat Detection,” via The Pig Site (2013)Returns to heat 18–24 days after service