How to calculate a cat's due date
A cat's due date is estimated by adding the average gestation length to the date of mating. Feline gestation averages about 63 to 65 days, with a normal full-term range of roughly 61 to 72 days. This calculator uses 63 days as the default, then also shows the day-61 and day-72 bounds so you know the full window in which healthy kittens may arrive:
Due date = mating date + 63 days. Because the exact day of conception within the fertile window is rarely known, the single "due date" is best read as the center of a due window, not a guaranteed delivery day.
Why the exact date is uncertain
A queen (a female cat) is an induced ovulator — ovulation is triggered by mating, and she may mate several times over a few days when in heat. Sperm can also survive in the reproductive tract for a day or more. As a result, the true fertilization date can differ from the observed mating date by a day or two, which is one reason the normal delivery range spans about 11 days.
Gestation timeline and milestones
- Days 1-17 (weeks 1-2): Fertilized eggs implant in the uterus; no outward signs.
- Around day 15-18: "Pinking up" — nipples become pink and slightly enlarged, often the first visible sign.
- Day 21 onward: A veterinarian can often palpate the fetuses; ultrasound can confirm pregnancy from about day 16-21.
- Weeks 5-6 (days ~30-42): Rapid fetal growth; the abdomen visibly enlarges. X-ray from about day 42-45 can count skeletons.
- Weeks 7-9 (days ~49-63): Kittens can be felt moving; the queen seeks out a nesting spot. A drop in rectal temperature below about 99°F (37.2°C) often precedes labor by 12-24 hours.
Signs labor is near
In the last day or two the queen may stop eating, become restless, vocalize, and settle in her nesting box. Average litter size is about 4 kittens (typically 1-8). If active straining lasts more than 20-30 minutes without a kitten, if more than about 2 hours pass between kittens, or if pregnancy exceeds day 70-72, contact your veterinarian promptly.