How long sheep are pregnant
Ewes are pregnant for about 145 days. NADIS puts the normal range at 143 to 147 days. So the first lambs can come 143 days after the tup goes in, and the last ewes served before he comes out will lamb up to 147 days after that.
How this is calculated
- First lambs: tup in + 143 days.
- Most likely date for ewes served on day one: tup in + 145 days.
- Last lambs: tup out + 147 days (or tup in + 147 days for a single date).
- Raddle groups: each colour covers the ewes marked during its 10 or 17 day spell. That group lambs from the first day of the spell + 143 days to the last day + 147 days.
The calculator uses the same range for every breed. Individual ewes can still lamb outside it, so keep watching the flock either side of the window.
Worked example
A smallholder puts the tup in on 5 November 2026 with a yellow raddle and changes colour every 17 days. The tup comes out on 10 December.
Lambing should start on 28 March 2027, with ewes served on the first day most likely to lamb around 30 March. Ewes marked yellow (served 5 to 21 November) should lamb between 28 March and 17 April. The flock should be finished by 6 May 2027.
When to step in or call the vet
- No progress after 30 minutes of strong straining once the water bag has burst: assist the ewe.
- More than an hour between lambs from the same ewe: consider helping.
- You can't deliver the lamb on your own: call the vet straight away.
- A prolapse: treat straight away and get veterinary advice.
- After lambing, a dull ewe off her food with a red-brown smelly discharge may have metritis.
From NADIS guidance on lambing. Your own vet's advice comes first.
Records and movements
Lambs need tagging and recording under your nation's sheep identification rules, which use different systems in England, Scotland, Wales and Northern Ireland. Check the current rules with your local animal health office or your nation's livestock movement service before lambing starts.