Add a standard sheep gestation length (default 147 days) to a ram-in or marking date to plan lambing — or count back from the week you want lambs on the ground.
Use this when you know when the ram went in (or saw a raddle/crayon mark) and need a lambing date for shed prep, shearing timing, and late-gestation feeding.
Sheep gestation averages about 147 days, with most ewes lambing within roughly 142–152 days. Breed, litter size, and ewe age move individual dates.
Forward mode adds gestation days to the breeding date. Reverse mode subtracts gestation days from the date you want ewes to lamb. The 147-day default is a planning average; change it to match your breed records.
lambing_date = breeding_date + gestation_days
breeding_date = target_lambing_date − gestation_days
window = result ± window_days
Bred 1 Oct 2026 at 147 days → due about 25 Feb 2027. With a ±5 day window, watch roughly 20 Feb 2027 – 2 Mar 2027.
Reverse check: to have ewes lamb on 25 Feb 2027, breed on 1 Oct 2026 (25 Feb 2027 − 147 days).
Assumptions: calendar-day arithmetic from a single breeding date; gestation length is a planning average you can change.
Limits: Ram exposure over a full cycle (about 17 days) or longer gives a spread of conception dates. Not a pregnancy diagnosis and not veterinary advice.
Responsibility: confirm pregnancy with your veterinarian and have facilities and supplies ready before the early edge of the window.
It is the common planning average for sheep. Early-maturing and prolific breeds can run a few days shorter; some fine-wool and late-maturing breeds run a few days longer.
Use the date of a recorded mark if you have it. Without marks, run the first day the ram went in and the day he came out — the two results bracket your lambing season.
Ewes carrying twins or triplets often lamb a little earlier than ewes carrying singles, which is one reason a ± window is useful.