# Sheep gestation: when is my ewe due?

Computes a ewe’s lambing date from the breeding date (148 days), the normal lambing window of 144 to 152 days, how many days along she is, and when to watch for heat if she did not settle.

- Page: https://www.acalculator.org/biology/sheep-gestation-calculator
- JSON spec: https://www.acalculator.org/biology/sheep-gestation-calculator.json
- Version: 8a9803e2ca3c

## Default answer

Example with the default inputs (Breeding date August 4, 2026, Today’s date October 3, 2026) on the example date Saturday, October 3, 2026: Your ewe is due to lamb about December 30, 2026, between December 26, 2026 and January 3, 2027.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| d | Breeding date | The day the ewe was bred (mated or inseminated). |
| on | Today’s date | The day to count from, to show how far along the ewe is. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| due | Estimated lambing date | The breeding date + 148 days. |
| earliest | Earliest normal lambing date | The breeding date + 144 days. |
| latest | Latest normal lambing date | The breeding date + 152 days. |
| days | Days along | Whole days from the breeding date to today’s date. |
| left | Days to the estimated lambing date | Whole days from today’s date to the estimated lambing date; negative once it has passed. |
| stage | Where she is now | The stage on today’s date, in one line. |
| heat | Next heat if she did not settle | The breeding date + 17 days, one estrous cycle later. |

## Method

Lambing date = breeding date + 148 days; normal window = breeding date + 144 to 152 days; next heat = breeding date + 17 days.

## Assumptions

- The estimate of 148 days is the gestation Alabama Extension plans with; the window of 144 to 152 days is from University of Missouri Extension.
- Days count from the breeding date as day 0. Breed and the number of lambs change the length a little.
- A ewe that did not settle comes back into heat about one estrous cycle after breeding; Merck gives 16 to 17 days, and the date uses 17.

## Worked examples

1. d = 2026-04-01, on = 2026-06-01 gives due = 2026-08-27, earliest = 2026-08-23, latest = 2026-08-31, days = 61, left = 87, heat = 2026-04-18, stage = Day 61 of about 148: 87 days to the estimated lambing date.. Source: Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period), https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03); University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days), https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03); Merck Veterinary Manual, Reproductive Physiology of Sheep (in ewes, estrous cycles average 16 to 17 days), https://www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-sheep/reproductive-physiology-of-sheep (retrieved 2026-10-03); 1 April 2026 + 144, 148 and 152 days.
2. d = 2027-11-01, on = 2028-03-30 gives due = 2028-03-28, earliest = 2028-03-24, latest = 2028-04-01, days = 150, left = -2. Source: Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period), https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03); University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days), https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03).

## FAQ

### How long is a sheep pregnant?

About 148 days, or 5 months. University of Missouri Extension gives a range of 144 to 152 days, and Alabama Extension plans lambing on a 148-day gestation.

### How is the lambing date worked out?

The calculator adds 148 days to the breeding date. The earliest and latest normal dates add 144 and 152 days. A ewe bred on 1 April 2026 is due about 27 August 2026.

### What if the ram was with the flock for weeks?

Type the day the ram went in for the first possible lambing date, then the day he came out for the last. Marking harnesses or crayons on the ram show which ewes were bred and when.

### When will she come back into heat if she is not pregnant?

Merck gives an estrous cycle of 16 to 17 days for ewes. The calculator shows the date 17 days after breeding; watch from a day before. No heat then is a first sign that she settled.

### What if my ewe goes past the latest date?

Call your vet. A ewe past day 152, or one that strains for a long time without a lamb, needs a check.

### Do breed and the number of lambs change the date?

A little. Ewes carrying twins or triplets often lamb a few days earlier than ewes with a single lamb, and breeds differ by a few days.

## Sources

- University of Missouri Extension, Breeding Season Considerations for Sheep and Goats, G2611 (the gestation period ranges between 144 and 152 days; October 2023). https://extension.missouri.edu/publications/g2611 (retrieved 2026-10-03)
- Alabama Cooperative Extension System, Reproductive Management: Dairy Goats and Sheep (Table 3: numbers based on a 148-day gestation period; August 2019). https://www.aces.edu/blog/topics/sheep-goats/reproductive-management-dairy-goats-and-sheep/ (retrieved 2026-10-03)
- Merck Veterinary Manual, Reproductive Physiology of Sheep (in ewes, estrous cycles average 16 to 17 days; updated March 2026). https://www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-sheep/reproductive-physiology-of-sheep (retrieved 2026-10-03)