Put in the date your ewe was bred and you'll get her lambing date back. Sheep carry lambs for about 147 days on average, though anywhere from 142 to 152 days is normal, so the calculator gives you a date range as well as a single due date. Pick your breed if you know it and the estimate tightens up.
Most flock owners who lose lambs don't lose them at birth. They lose them because nobody was watching that week. Knowing your lambing window ahead of time is what lets you shear on schedule, get the vaccinations in, and be in the barn when it counts.
Enter a breeding date above and press Calculate lambing date, your lambing date, progress and milestone timeline appear right here.
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Key dates from mating to lambing. Completed steps are marked; the next action is highlighted.
Three inputs, one answer. Here's what each field does and what to watch out for.
Enter the day the ewe was covered by the ram or artificially inseminated. Not sure of the exact day? Use the first day the ram went in, the calculator then gives the front edge of your lambing period. A marking harness makes it precise: change the crayon colour every 16 to 17 days to track which cycle each ewe settled on.
Breed shifts the date by a few days. Dorpers lamb around 145 days; Merinos and Romneys run to 148 or 150. Unsure or crossbred? Leave it on 147. You can also set your own number under Advanced, your flock records beat any breed average.
You get one bold date, the most likely day, plus the earliest and latest she could go. Plan around the range and its first day, not the single date. The calculator also gives the working dates behind it: when to scan, shear, change feed and vaccinate.
The tool needs one thing, the date the ewe was bred. Not sure of the exact day? Use the day the ram went in and read the answer as her earliest lambing date.
↑ Try it nowA ewe is pregnant for about five months. In days, that's 142 to 152, with 147 sitting in the middle as the working average that almost everyone uses.
Five months is the answer you’ll get if you ask a shepherd in the yard. Twenty-one weeks is the same answer said differently, and it’s the one you’ll hear from British and Irish farmers more often. All three ways of saying it describe the same stretch of time, so don’t get thrown when different sources phrase it differently.
The 142 to 152 window covers most ewes on most farms. It isn’t a hard boundary. Montana State’s extension service puts the typical range at 144 to 151 days and notes that individual pregnancies have come in as short as 138 and as long as 159. Those outliers are rare and you’ll probably never see one, but a ewe lambing at 143 or 153 days shouldn’t send you into a panic.
Because five months is a little under half a year, a ewe is physically capable of lambing twice in twelve months. Most flocks don’t run that way, and there’s a good reason for it, which we get into further down.
For the full picture, read how long sheep are pregnant, the gestation length of each breed, and how litter size shifts the date.
the yard answer
British & Irish
the calculator
The calculation is simple enough to do on the back of a feed bag.
Breeding date + 147 = Lambing date
That’s it. Count 147 days forward from the day she was bred and you’ve got your due date.
So you’d want the lambing shed ready by mid February, not the last week of it.
Add five months to the breeding date, then knock off a few days. Five months from the 1st of October is the 1st of March, and 147 days actually lands on the 25th of February, so the shortcut runs you four or five days late.
Fine for a rough answer, not good enough for planning your shearing.
Swap 147 for whatever figure fits your flock. A Dorper breeder would use 145. A Babydoll breeder would too. The registry calculators for those breeds are built on 145 days rather than 147, which is why their answers differ from a general sheep calculator by a couple of days.
In the calculator above, open Advanced options to set your own gestation length (138–155 days). Your number always wins over the breed default.
Most calculators ignore breed and give everyone the same 147 days. That's a reasonable default, but it's not the whole story. Body size, genetics, and how many lambs a breed typically carries all pull the number around a little.
| Breed | Type | Average Gestation |
|---|---|---|
| Suffolk | Meat | 145–148 days |
| Texel | Meat | 145–148 days |
| Dorper / White Dorper | Meat | ~145 days |
| Hampshire | Meat | 145–148 days |
| Border Leicester | Dual-purpose | 145–148 days |
| Katahdin | Hair | 145–148 days |
| Lacaune | Dairy | 145–150 days |
| East Friesian | Dairy | 145–150 days |
| Merino | Wool | 147–150 days |
| Romney | Wool | 147–150 days |
| Rambouillet | Wool | 147–150 days |
| Babydoll Southdown | Small | ~145 days |
| Ouessant | Small | 149–155 days |
Select any of these in the calculator above and its gestation length loads automatically.
Meat and terminal breeds sit at the shorter end, 145 to 148 days. The American Dorper Sheep Breeders’ Society calculates Dorpers at 145. The ram matters too: New Mexico State University research found ewes bred to black-faced or meat-type rams carry shorter than those bred to white-faced rams.
Dairy ewes run 145 to 150 days. East Friesians and Lacaunes are prolific and often carry twins or triplets, and bigger litters shorten gestation, a triplet-bearing Friesian can lamb three to four days early. For milking flocks the date sets the whole lactation calendar.
Wool breeds are the longest mainstream type, 147 to 150 days. Merinos and Romneys sit in that band and lean toward singles, which stretches the number. A heavy fleece on a ewe about to lamb is a problem, so shearing timing matters here.
Small breeds break the pattern, a smaller sheep does not mean a shorter pregnancy. Babydoll Southdowns run 145 days; Ouessants, the world’s smallest breed, run 149 to 155 days, longer than a Suffolk. Use the breed number, not 147: on a small breed that gap is ten days.
Breed is one piece. Here's the rest of what moves the number.
Genetics run deeper than the breed label. Individual ewe lines carry consistently short or long. Check your own lambing records, the same ewes often lamb early or late every year, and that pattern beats any published average.
★ Biggest factor
Litter size is the biggest factor, and it works backwards: more lambs means a shorter pregnancy. A triplet-bearing ewe lambs three to five days before a single-bearing one. Scan to find your multiples, group them, feed them properly, and expect them first, they also carry the highest twin-lamb-disease risk.
Maiden ewes usually carry a single; twins become the norm from the second lambing, peaking between three and six years old. Bigger litters lamb earlier, so a mature ewe often beats a maiden bred the same day. Breed ewe lambs only once they reach 65 to 70 percent of mature body weight, or conception drops and lambs come weak.
Feed barely shifts the due date, but poor feeding in the last six weeks causes pregnancy toxaemia (twin lamb disease), which can kill the ewe and lambs together. Twin- and triplet-bearing ewes are most at risk as their energy demand doubles in the final month. Stress from cold snaps, dogs or rough handling can also trigger early lambing.
The due date is only useful if you work backwards from it. Here's what the 147 days actually look like on a working farm.
Scan between day 45 and 90 for a reliable lamb count. The count matters more than a yes/no: it lets you split ewes into feeding groups, so singles and triplets each get the right ration. Scanning usually pays for itself in feed savings alone.
Read: pregnancy scanning →The first two thirds are quiet, the lamb grows slowly and grass is usually enough. Hold body condition score around 3 going into late pregnancy. A ewe too thin at day 100 cannot be fixed by day 130, and a fat ewe risks a hard lambing. Check backbone and ribs by hand every few weeks.
Read: body condition scoring →From day 105 the lamb grows fast, 70 percent of birth weight forms now, while it crowds the abdomen and the ewe eats less bulk. Feed better quality, not just more. Give the clostridial booster four to six weeks out: it passes antibodies through the colostrum to protect the lamb.
Read: clostridial vaccination →Crutch or shear four to six weeks before lambing, not the week before. A clean ewe is easier to lamb and inspect, and the lamb can find the teat. Set up the lambing shed in the same window: pens, iodine, a stomach tube, frozen colostrum, and a warming box for cold climates.
Read: lambing prep checklist →Honestly? For the first three months, you often can't. Not by looking.
A ewe doesn’t show visibly until roughly six weeks before she lambs, so for most of the pregnancy there’s nothing obvious to see. Shepherds have historically got around this by assuming the ram covered everybody and planning accordingly, which works, but it’s blunt.
Closer to the day, learn the signs a ewe is close to lambing and when a difficult lambing needs your help.
One for the wool breeds: a marking harness crayon stains the fleece. If wool quality matters to your operation, talk to your buyer before you strap a raddle on the ram.
The only method that tells you how many lambs she’s carrying, and the reason most commercial flocks scan.
The crayon marks every ewe he covers, so you know who was served and roughly when. Change colours every couple of weeks and you can sort your ewes into lambing groups without a scanner.
A ewe cycles every 16 or 17 days. If she doesn’t come back into season three weeks after being served, she’s probably settled. Requires you to be watching, which is why the harness is easier.
Around three months in she starts to round out and carry herself heavier, though a fat empty ewe can fool you.
Her udder fills in the last stretch before lambing. Useful for telling you she’s close, useless for telling you she’s pregnant three months out.
= how reliable each method is
Enter one breeding date and get the due date, the 142–152 day window and a dated milestone plan, scanning, feeding, vaccination, shearing and lambing.
Common questions about sheep pregnancy, lambing and using this calculator.
Around 147 days, which is roughly five months or 21 weeks. The normal range is 142 to 152 days. Individual ewes have been recorded as short as 138 days and as long as 159, but those are unusual. For planning purposes, 147 days from the breeding date is the number to work with, and you should treat the whole 142 to 152 window as your lambing period rather than banking on a single day.
Most ewes have one to three lambs, and twins are the most common outcome once a ewe has lambed before. First-time ewes usually have a single. Older ewes in good condition can produce five or six, though a ewe can realistically only feed two herself, so triplets and above mean you'll be fostering a lamb onto another ewe or bottle-feeding it. Ewes throw their biggest litters between three and six years of age.
Biologically, yes. A 147 day pregnancy leaves enough room in the calendar. In practice most flocks lamb once a year, because sheep are seasonal breeders and only cycle naturally in autumn as the days shorten. Some breeds cycle out of season more readily than others, and accelerated lambing systems (three lamb crops in two years) do exist. They need tight management and good feeding, and they are hard on the ewes, so most producers stick with one crop a year.
Autumn, for most flocks. Fertility peaks as the days get shorter, which is why breeding usually happens between roughly September and November in the northern hemisphere and lambs arrive in spring when there is grass to feed on. For the individual ewe, wait until she is grown. Small and medium breeds are usually ready around six to eight months, larger breeds closer to eight to twelve months. Age alone is not enough: she needs to be at roughly 65 to 70 percent of her mature body weight before the ram goes in, or you will get poor conception and weak lambs.
It is an estimate, and its accuracy comes down entirely to how good your breeding date is. Give it an exact service date and the lambing date will usually land within a few days. Give it a rough guess and you will get a rough answer back. No calculator can account for what happens inside a particular ewe. Litter size can shift her lambing date by several days, and nobody knows how many lambs she is carrying until she is scanned. Use the date as the middle of your lambing window, get everything ready by the earliest date in the range, and let the ewe do the rest.