Why mating dates are loose
- Sperm outlives the mating. It can survive for several days in the female tract before the eggs are ready.
- Eggs need time to mature. A dog’s eggs need about two to three days after ovulation before they can be fertilized.
- Ovulation is not on a fixed day of heat. So a mating on a given day tells you little about when conception happened.
Accuracy by method
| Date you enter | Average | Normal window | Precision |
|---|---|---|---|
| Single mating date | 63 days | 56–70 days | ±7 days |
| Ovulation (progesterone) | 63 days | 62–64 days | ±1 day |
| LH surge peak | 65 days | 64–66 days | ±1 day |
| Diestrus day 1 (cytology) | 57 days | 55–59 days | ±2 days |
How to tighten the date
If she has not been mated yet, ask your vet about progesterone testing. If she already has, an ultrasound at about day 25 to 30 can estimate gestational age, and an X-ray after day 45 to 50 shows how developed the skeletons are. Both are wider estimates than hormone testing.