Gestation CalculatorSwine Gestation Calculator
Enter the date the sow or gilt was bred. You get the farrowing date, the window and a pig pregnancy calendar.
Estimated due date
Sat, Apr 25, 2026
Normal window: Apr 25, 2026 to Apr 28, 2026
- Today
- Not bred yet
- Days to go
- 114
Pregnancy calendar and key dates
| Date | Day | What to do or expect |
|---|---|---|
| Jan 19, 2026 | 18 | Watch for return to heat (days 18 to 24) [source] |
| Jan 28, 2026 | 27 | Ultrasound pregnancy check possible [source] |
| Mar 14, 2026 | 72 | Last 6 weeks: window for pre farrowing vaccines (ask your vet) [source] |
| Apr 24, 2026 | 113 | Nest building often starts in the last 24 hours [source] |
| Apr 25, 2026 | 114 | Normal farrowing window opens: have pens, bedding and supplies ready [source] |
| Apr 25, 2026 | 114 | Estimated due date [source] |
| Apr 28, 2026 | 117 | Normal window closes: call your vet if no birth [source] |
Check with your vet. This is an estimate from average gestation lengths. Your vet can confirm the pregnancy, date it more closely, and tell you when to call for help at birth.
How long is a pig pregnant?
A sow is pregnant for about 114 days, often remembered as 3 months, 3 weeks and 3 days. The Merck Veterinary Manual reports that modern herds now average 115 to 116 days, plus or minus 1, from first service, so this tool shows a 114 to 117 day window.
University of Missouri Extension uses 114 days in its farrowing table. Merck notes that average length has been rising and is slightly shorter in sows with larger litters.
| Source | Figure |
|---|---|
| University of Missouri Extension | 114 days average |
| Merck Veterinary Manual (2026) | 115 to 116 days, plus or minus 1 |
How to use the farrowing calculator
Enter the first service date. The tool adds 114 days for the farrowing date and shows the window out to day 117. If your herd records show a different average, use the window to plan crate moves and staff.
Merck notes good records are key, since the herd average and each sow's breeding date are needed for planning.
Sow due date formula
Farrowing date equals breeding date plus 114 days. A sow bred on January 1, 2025 is due April 25, 2025, which matches the University of Missouri gestation table. The window runs to breeding date plus 117 days.
Farrowing date = breeding date + 114 days
Key dates in a pig pregnancy
Watch for a return to heat 18 to 24 days after service. Real time ultrasound can confirm pregnancy from about 27 days with over 95% accuracy. Merck advises giving pre farrowing vaccines in the last 6 weeks to boost colostrum antibodies.
- Days 18 to 24: no return to heat suggests pregnancy, but Merck says this is only 75% to 85% accurate.
- First 30 days: embryos are most at risk. Avoid moving, mixing and heat stress.
- Last 24 hours: restlessness and nest building are common.
Questions people ask
Is the 3 3 3 rule right?
Three months, three weeks and three days is about 114 days. It is a handy guide. Merck reports modern herds average a day or two longer.
Do gilts and sows differ?
Our sources give one figure for both. Merck says length is slightly shorter in sows carrying larger litters.
When should I call the vet?
Ask your vet before day 114 about a farrowing plan. Call if a sow strains with no piglet, or if she passes the window.
Other animals
- Cow: 283 days
- Horse: 340 days
- Dog: 63 days
- Goat: 150 days
- Sheep: 147 days
- Cat: 65 days
- Rabbit: 31 days
- Alpaca: 342 days
References
- Care of Pigs From Farrowing to Weaning (G2500). University of Missouri Extension.
- Breeding Management of Pigs. Merck Veterinary Manual (R. V. Knox, University of Illinois), reviewed July 2026.
- Approximate Gestation Periods (table). Merck Veterinary Manual.