Instrument № 08 - Farm

Hog
Gestation

Estimated farrowing date from a breeding date - or work it backwards. With pregnancy check, move-to-farrowing, and pre-farrowing milestones laid out on the same timeline.

See the math behind this calculator

Standard gestation
114 days

Old farmer rule
3 mo · 3 wk · 3 d

Typical window
± 2 days

Direction

Dates

Breeding date

Parameters

Gestation length (days)

Window (± days)

Wean age (days)

Wean schedule preset

Estimated farrowing date -

Farrowing window -

Breeding date -

Pregnancy check (~d30) -

Move to farrowing (~d110) -

Pre-farrow vaccine (~−21d) -

Wean date -

How it works

Pigs are remarkably consistent. The average gestation across breeds and parities lands almost exactly on 114 days from breeding to farrowing.

Add 114 days to a breeding date and you have a due date. Subtract 114 from a target due date and you know when to breed. Build the rest of the husbandry calendar around those two anchors.

due_date = breeding_date + 114 days

Frequently asked

How accurate is the due date?

Within two days for most healthy sows. Gilts (first-time mothers) sometimes farrow a day or two earlier. Older sows and certain heritage breeds may run a day or two later. Big litters tend to come slightly early.

When should I do a pregnancy check?

Around day 28–30 by ultrasound. Blood tests can confirm pregnancy as early as day 21. Visual signs (no return to heat by day 21, body changes) are unreliable until later.

What signs mean farrowing is imminent?

Milk in the teats (12–24 hours out), visible nest-building behavior (6–12 hours), restlessness and breathing changes (1–4 hours), discharge from the vulva (under 1 hour). When milk drips freely, piglets are typically within an hour or two.

Show the working

Gestation in pigs is famously regular, which is what makes this simple date arithmetic reliable enough to plan around. If any of it looks wrong, it might be - tell us what we got wrong.

Farrowing date from breeding date due = bred date + 114 days

Breeding date from a target farrowing bred = due date − 114 days

Farrowing window window = due date ± the days you set

Management dates

pregnancy check = bred + 21 days
move to farrowing = due − 7 days
weaning = due + weaning age

Constants used

114 days — average gestation — the old rule of thumb is three months, three weeks and three days
± 2 days — default farrowing window, editable
21 days — default weaning age, editable

114 days is an average. Individual sows commonly run 111 to 117, and gilts tend to farrow slightly earlier than mature sows.

The sources

Swine gestation is usually taught as the three-three-three rule, and this page uses the 114 days that mnemonic actually adds up to. The source is worth reading because it does not quite agree with itself on the last day.

Three months, three weeks, three days 90 + 21 + 3 = 114 days

Hines E, Chandool J. Developmental Milestones During Pig Gestation. Penn State Extension. Gives gestation as about 115 days, or 3 months, 3 weeks and 3 days, and sets out the five developmental phases across that period.

Note the small disagreement inside the source itself - the three-three-three mnemonic adds to 114 days while the text alongside it says about 115. Published figures generally sit between 112 and 116. This page defaults to 114 because that is what the mnemonic computes, and the field is editable because your herd's own average beats anyone else's.