Every calculator on this site works the same way. You enter a date, and we add that animal’s average pregnancy length to get the due date. Where a normal range is well established, we also show the earliest and latest normal days.
The figures we use
| Animal | Due date (average) | Normal range shown | Counted from |
|---|---|---|---|
| Dog | 63 days | 58–72 days (62–64 from ovulation) | First mating, or vet-timed ovulation |
| Cat | 65 days | 64–66 days | Mating |
| Rabbit | 31 days | 31–33 days | Mating |
| Horse | 340 days | 320–370 days | Last breeding |
| Cow | 283 days | About 279–286 days for most beef cattle | Breeding or insemination |
| Goat | 150 days | 145–155 days | Breeding |
| Sheep | 147 days | 144–152 days | Breeding |
| Pig | 115 days | 114–117 days | First service |
Why we show a range
An average is only the middle of what is normal. Breed, litter size, the season and the animal herself can all move the birth by days or, in horses, by weeks. Showing the range helps you plan without panicking when the due date passes.
How dates are counted
- Day 0 is the date you enter. The due date is that date plus the average number of days.
- For dogs bred more than once, the window runs from 58 days after the first mating to 72 days after the last.
- If your vet timed ovulation, the dog calculator switches to the tighter 62–64 day window.
- All dates are worked out in your browser. Nothing you enter is sent to us.
Our references
- Merck Veterinary Manual: whelping and queening in dogs and cats; breeding management of dogs and cats; breeding and reproduction of rabbits; pig and goat reproduction pages.
- Extension Horses (Cooperative Extension) and Oklahoma State University Extension: mare gestation and foaling.
- Oklahoma State University Extension: beef cattle gestation and calving management.
- Montana State University and New Mexico State University Extension: sheep reproduction.
- Eilts and others, “Factors affecting gestation duration in the bitch” (764 litters).
Limits of any calculator
A due date is an estimate. It cannot tell you whether an animal is pregnant, how many young she carries or whether the birth will be normal. Please see your vet to confirm a pregnancy and plan for the birth. Read our disclaimer for more.