Swine Gestation Calculator - Calculate Pig Farrowing Dates
Free swine gestation calculator for pig farmers. Enter breeding date to calculate accurate farrowing dates using the 114-day gestation period. Instant results.
Swine Gestation Calculator
Calculate the expected farrowing date based on the breeding date.
Gestation Period
Documentation
What is a swine gestation calculator?
A swine gestation calculator is a tool that estimates when a pregnant pig will give birth. It works out the expected farrowing date (the day a sow delivers her piglets) by adding the standard 114-day pig pregnancy length to the date of breeding or insemination.
How pig gestation works
Domestic pigs (Sus scrofa domesticus) have one of the most predictable pregnancies of any farm animal. The average gestation length is 114 days from breeding to farrowing. Most sows farrow somewhere between 111 and 117 days, so a few days of variation on either side of the calculated date is normal.
Farmers sometimes use the phrase "three months, three weeks, and three days" as a memory aid for 114 days. It is a rough guide rather than an exact formula, since calendar months differ in length. A calculator that adds 114 calendar days gives a more precise answer.
Several factors can shift the exact length of a pregnancy within the normal range:
- Breed
- Age and parity (number of previous litters) of the sow
- Litter size
- Nutrition
- Temperature and other environmental conditions
How to calculate a pig's farrowing date
The formula is simple:
Farrowing date = Breeding date + 114 days
To use it, count 114 calendar days forward from the day the sow was bred or artificially inseminated. This calculation automatically carries over different month lengths and leap years, because it works with actual calendar days rather than fixed 30-day months.
Example
A sow is bred on January 1, 2023. Adding 114 days lands on April 25, 2023. That April 25 date, not simply "four months later," is the expected farrowing date, because January, February, and March do not all have the same number of days. In a leap year, the same January 1 breeding date works out to April 24 instead, since the extra day of February shifts the count by one.
Key stages of gestation
The table below lists commonly cited approximate milestones during the 114-day period. Individual sows can vary.
| Day after breeding | What typically happens |
|---|---|
| 0 | Breeding or insemination |
| 12–14 | Embryos begin attaching to the uterine wall |
| 25–30 | A fetal heartbeat can usually be detected by ultrasound |
| 30 | Fetal skeletons begin to calcify |
| 57 | Midpoint of gestation |
| 90–100 | Mammary glands become visibly developed |
| 108–111 | Sow is moved to a clean farrowing area |
| 112–114 | Nesting behavior appears; milk can often be expressed from teats |
| 114 | Expected farrowing date |
Preparing for farrowing
Most farrowing preparation happens in the final two weeks of gestation.
- About a week before the due date: clean and disinfect the farrowing area, set up heat lamps or heating pads for piglets, and move the sow into the farrowing space.
- In the final days: watch the sow for nesting behavior, keep bedding clean and dry, and have supplies ready, such as clean towels, iodine for piglets' navels, and a way to keep piglets warm.
- During farrowing: keep the area quiet, let piglets nurse for colostrum as soon as possible, and record how many piglets are born alive and stillborn.
Signs that farrowing is near
A sow that will farrow within about a day often shows some of these signs:
- Restlessness and nest-building behavior
- Milk that can be expressed by hand from the teats
- A swollen, reddened vulva
- Reduced appetite
- A drop in body temperature of roughly 1°F (about 0.5°C) below normal
- Frequent lying down and standing up
Frequently asked questions
How long are pigs pregnant? On average, 114 days from breeding to farrowing. Normal farrowing usually falls between 111 and 117 days after breeding.
What is the "3-3-3" rule for pig gestation? It is a traditional shorthand: three months, three weeks, and three days. It is a memory aid, not an exact count, since months vary in length. Counting 114 calendar days gives the accurate date.
What if a sow has not farrowed by the calculated date? A few days past the estimate is common. If a sow has not farrowed by around day 118 to 119, it is reasonable to check her closely for signs of labor and to contact a veterinarian, since a long delay can signal a complication.
Does the calculation account for leap years? Yes. Adding 114 calendar days to a breeding date automatically accounts for February 29 in a leap year and for months of different lengths, since it counts actual days rather than fixed-length months.
Can this calculator be used for mini pigs or pot-bellied pigs? Yes. Miniature pig breeds have a gestation length close to that of standard production pigs, typically around 112 to 114 days. It is reasonable to prepare a few days early with these breeds.
How soon after farrowing can a sow be bred again? Commercial sows are usually bred again after weaning, not right after farrowing. A typical lactation lasts about three to four weeks. Sows commonly return to estrus around four to seven days after weaning, and breeding then starts the next pregnancy.