Swine Gestation Calculator — Expected Farrowing Date
Enter the breeding or confirmed service date and pig breed to get the expected farrowing date, gestation length, and a visual timeline of pregnancy progress. The famous "3-3-3 rule" (3 months, 3 weeks, 3 days) gives the 114-day average.
Breeding / service date
Reference date (today)
Breed
How does this calculator work?
Pig gestation averages 114 days (the "3-3-3 rule": 3 months, 3 weeks, 3 days), with breed-specific variation from 113 (Chester White) to 116 days (Mangalitsa). Add the breed's gestation length to the breeding date to find the expected farrowing date, then prepare the farrowing pen 5–7 days before.
Formula
How this is calculated
Pig gestation averages 114 days — a figure easy to remember as 3 months, 3 weeks, and 3 days (the "3-3-3 rule"). Actual duration varies slightly by breed: Chester White tends toward 113 days while Mangalitsa can reach 116. The breed averages used here are drawn from peer-reviewed swine production references; actual farrowing can occur 3–5 days either side of the predicted date.
The calculator adds the selected breed's gestation length to the entered breeding or confirmed insemination date to produce the expected farrowing date. For artificial insemination (AI), use the insemination date. For natural service, use the last observed mating date. A sow may be rebred at her next oestrus cycle (roughly 21 days post-weaning), so accurate breeding records are essential for timely pre-farrowing preparation.
The gestation timeline shows progress from breeding to the expected farrowing window. Begin close monitoring from about 5 days before the predicted date. Key signs of approaching farrowing include udder engorgement and milk let-down 24 hours before, nesting behaviour, and restlessness. Litter size, parity number, ambient temperature, and nutrition can all shift the actual date slightly from the prediction.
Frequently asked questions
The 3-3-3 rule is a practical mnemonic: swine gestation lasts approximately 3 months, 3 weeks, and 3 days — which adds up to about 114 days. It is a useful on-farm shortcut, though individual sows and breeds can vary by ±3–5 days around that figure.
Move the sow to a clean, pre-warmed farrowing crate or pen 5–7 days before the predicted farrowing date. This allows her to settle, reduces stress, and gives time to spot any pre-farrowing health issues. Ensure creep heat (around 32 °C for piglets) and colostrum access are ready before the first pig is born.
If the breeding date is uncertain, a rectal or transabdominal ultrasound performed by a veterinarian at 25–35 days post-mating can confirm pregnancy and estimate gestational age. Blood progesterone testing or urine oestrone sulphate assays are also used to confirm pregnancy from about 28 days onwards.
Also known as
TG we-Calculate Editorial Team. (2026). Swine Gestation Calculator — Expected Farrowing Date [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/swine-gestation-calculator
TG we-Calculate Editorial Team. "Swine Gestation Calculator — Expected Farrowing Date." TG we-Calculate. 2026. https://we-calculate.com/calculator/swine-gestation-calculator.
TG we-Calculate Editorial Team, "Swine Gestation Calculator — Expected Farrowing Date," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/swine-gestation-calculator
@misc{wecalculate_swine_gestation_calculator, title = {Swine Gestation Calculator — Expected Farrowing Date}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/swine-gestation-calculator}}, year = {2026}, note = {TG we-Calculate} }
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