What this calculator does
Sow gestation is close to 114 days, and the traditional way of remembering it is three months, three weeks and three days. Adding that to the breeding date gives the expected farrowing date.
Swine gestation is unusually consistent, which is why a single figure works where a horse needs a three-week window. Most sows farrow within a day or two either side of 114 days, so the date is genuinely useful for planning rather than merely indicative.
The formula
114 days are added to the breeding date entered. That figure is the widely used average for commercial swine, and the three months, three weeks, three days mnemonic gives the same result within a day depending on which months are involved.
| Term | Meaning |
|---|---|
| Farrowing | Giving birth, in pigs. |
| 114 days | The standard average gestation length for sows. |
| Three-three-three | The mnemonic: three months, three weeks and three days from breeding. |
| Breeding date | The date of service or insemination, which the count starts from. |
The inputs explained
| Field | What to enter |
|---|---|
| Breeding date | The breeding or insemination date. Where service happened over more than one day, the first service is the usual reference. |
When to use it
Planning farrowing accommodation
Sows are moved into farrowing crates or pens several days before the due date, and that move has to be scheduled against an expected date.
Scheduling labour and supervision
Farrowing benefits from supervision, and knowing which week it falls in is how staffing is arranged on a commercial unit.
Managing a batch farrowing system
Batch systems breed groups together so they farrow together, and the calculation confirms the group will land in the intended week.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What farrowing date does each breeding date give?
Three breeding dates spread through the year with their expected farrowing dates.
| Breeding date | Expected farrowing date | Gestation length used |
|---|---|---|
| 2026-01-01 | 25 Apr 2026 | 114 days |
| 2026-04-15 | 7 Aug 2026 | 114 days |
| 2026-09-01 | 24 Dec 2026 | 114 days |
Questions
How long are pigs pregnant?
About 114 days, or three months, three weeks and three days. The normal range is roughly 111 to 120 days, but the great majority farrow within a day or two of 114, which makes swine gestation among the most predictable of the farm species.
Does litter size affect gestation length?
Slightly. Larger litters tend to be carried marginally shorter, and gilts sometimes farrow a little earlier than mature sows. The effect is small enough that 114 days remains the working figure for planning.
What if the sow goes past the due date?
A day or two over is unremarkable. Beyond about 116 to 117 days is worth veterinary attention, since prolonged gestation raises the risk of stillbirths and of the piglets becoming too large to deliver easily.
When should the sow move to the farrowing area?
Commonly three to seven days before the expected date, giving her time to settle and allowing the space to be cleaned and warmed first. Moving her too late adds stress at exactly the wrong point.
For feed efficiency through the growing phase that follows, see the feed conversion ratio calculator. For comparing feeds of different moisture content, see the dry matter basis calculator.