What this calculator does
Gestation length varies enormously between species and much less within them. A rabbit is about 31 days, a dog 63, a goat 150 and a horse 340. Adding the species average to the breeding date gives a due date, which is all this calculator does.
The window matters more than the date. A dog is fairly predictable at 63 days give or take a few, while a horse varies by weeks in either direction, so a single date for a mare is close to meaningless without the range beside it. The calculator gives both.
The formula
The species average gestation length is added to the breeding date to give the expected due date, and the typical range for that species is applied either side to give the likely window. The figures are published species averages, and individual animals vary, particularly in species with naturally wide ranges.
| Term | Meaning |
|---|---|
| Gestation | The period from conception to birth. |
| Breeding date | The date of mating, taken here as the starting point. Where mating happened over several days, the middle of that period is the usual choice. |
| Likely window | The range around the average within which most births for that species occur. |
The inputs explained
| Field | What to enter |
|---|---|
| Animal | The species. Gestation lengths differ far too much between species for a single figure to work. |
| Breeding / mating date | The breeding date, or the middle of the mating period if it covered several days. |
When to use it
Planning for a litter or foaling
Knowing roughly when to have everything ready, and when to start watching closely, is the ordinary reason for the calculation.
Arranging veterinary support
Booking a check or having someone on call works from the window rather than the single date, particularly for species with a wide natural range.
Working backwards from an expected date
Where the due date is known and the breeding date is not, subtracting the species average gives an approximate conception date.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How long is gestation in each species?
The same breeding date of 1 January 2026 applied across six species.
| Species | Average gestation length | Expected due date | Likely window |
|---|---|---|---|
| Rabbit | 31 days | 1 Feb 2026 | 29 Jan 2026 – 5 Feb 2026 |
| Dog | 63 days | 5 Mar 2026 | 28 Feb 2026 – 10 Mar 2026 |
| Cat | 64 days | 6 Mar 2026 | 5 Mar 2026 – 7 Mar 2026 |
| Goat | 150 days | 31 May 2026 | 26 May 2026 – 5 Jun 2026 |
| Cow | 283 days | 11 Oct 2026 | 7 Oct 2026 – 15 Oct 2026 |
| Horse | 340 days | 7 Dec 2026 | 17 Nov 2026 – 6 Jan 2027 |
Questions
How long are dogs pregnant?
About 63 days from mating, with most litters arriving between 58 and 68 days. The variation comes largely from when in the fertile period conception actually happened, since sperm can survive several days and the mating date is not necessarily the conception date.
Why is the horse window so wide?
Because equine gestation genuinely varies by several weeks. An average of about 340 days covers a normal range from roughly 320 to 370, influenced by the sex of the foal, the season of conception and the individual mare. A precise date for a mare is not a meaningful thing to give.
Should I count from mating or from ovulation?
This calculator counts from the date you enter, which is normally the mating date. Where ovulation timing is known, as it often is for planned dog breeding, counting from ovulation is considerably more accurate and the expected date shifts accordingly.
What if the due date passes?
Speak to a vet. Going meaningfully past the expected window is a reason for a check rather than for waiting, and the threshold for concern differs by species. The calculator gives an estimate, not a clinical judgement.
For a dog heat cycle and its fertile window, see the dog heat cycle calculator. For the cost of the animal once it arrives, see the pet cost calculator.