Guinea pigs carry their pups for 59 to 72 days, unusually long for a rodent, and the exact length depends heavily on how many pups are in the litter. Enter the breeding date and this calculator gives you the earliest realistic delivery date, the typical due date, and the outer edge of normal, so you know roughly when to start watching closely.
Why the Window Is So Wide
Most rodents commonly kept as pets, hamsters, mice, rats, gestate in under three weeks. Guinea pigs are a real outlier at roughly nine to ten weeks, and unlike most mammals, litter size and gestation length move in opposite directions: a sow carrying a large litter of four or five pups typically delivers earlier, often in the 59 to 63 day range, because the pups compete for limited space and resources in the womb and growth slows as a result. A sow carrying a single pup, by contrast, can run the full length of the window and sometimes even push past 70 days, since that one pup has room to keep growing largely unimpeded. This calculator's three dates (59, 65, and 72 days from breeding) reflect that real spread rather than pretending guinea pigs deliver on a fixed schedule the way a due-date calculator for a single-litter-size species might.
The First-Time Sow Age Limit: A Real Danger, Not a Suggestion
This is the single most important fact for anyone breeding guinea pigs, and it is worth treating as a hard rule rather than general advice. A female guinea pig's pelvic bones are joined by a flexible ligament called the pubic symphysis, which needs to widen during labor to let pups pass through. That ligament stays flexible enough to widen only in sows that have their first litter before roughly 6 months old (some sources put the safe cutoff slightly later, around 7 to 8 months, but 6 months is the conservative, widely-used guideline). After that age, if she has never given birth, the pelvic bones fuse into a permanently rigid joint that will not widen for delivery. A first pregnancy in an older, previously unbred sow is a genuine emergency risk: the pups often cannot pass through the birth canal at all, and dystocia (obstructed labor) in guinea pigs frequently requires an emergency C-section and can be fatal to the sow without one. If you are planning to breed a female guinea pig for the first time, her age at the moment of breeding, not just her age at delivery, needs to be under that 6-month mark.
Signs Delivery Is Close
In the last few days before delivery, a sow's abdomen visibly widens and her pelvic bones separate enough to feel as a gap on either side of the spine near the tail, a change you can check for gently starting around day 55 to 60. She may also become notably less active and eat less in the final 24 to 48 hours. Labor itself is usually fast for guinea pigs, often under 30 minutes per pup, and pups are born fully furred with eyes open and able to move almost immediately, unlike the blind, hairless newborns of most other pet rodents. If a sow appears to be actively straining for more than 15 to 20 minutes without producing a pup, that warrants an urgent call to an exotics vet.
How to Use This Calculator
Enter the date the breeding or mating occurred. The calculator adds 59, 65, and 72 days to give you the earliest possible delivery, the typical average, and the latest date still considered within normal range. If today's date is past day 72 since breeding with no delivery yet, the calculator flags it as a reason to contact a vet.
Frequently Asked Questions
Can I estimate litter size from the due date?+
Only roughly. A due date on the earlier end of the window suggests a larger litter is more likely, and a date near day 70 to 72 suggests a smaller litter, often just one pup, but this is a tendency, not a reliable prediction method on its own.
Is it safe to breed a guinea pig older than 6 months for the first time?+
Generally no. Once the pelvic bones have fused, a first pregnancy carries a significantly elevated risk of fatal obstructed labor. This applies specifically to first pregnancies, a sow that has already delivered once before can typically be bred again safely at an older age.
How many pups do guinea pigs usually have?+
Litters typically range from one to six pups, with two to four being most common. As noted above, litter size and gestation length are inversely related.
Watch the calendar, but watch the sow's age even more closely.
The 59 to 72 day window gives you a realistic planning range, but the pelvic fusion age limit is the fact that actually protects the sow's life. If you're unsure how old your sow was at breeding, check her age with the Guinea Pig Age Calculator before anything else.
Past day 72 with no delivery, or any sign of prolonged straining, call an exotics vet immediately.
Sources and References
- RSPCA. Guinea Pig Breeding and Welfare Guidance. rspca.org.uk. Accessed August 2026.
- Merck Veterinary Manual. Reproduction in Guinea Pigs (Cavies), including pelvic symphysis fusion age and dystocia risk. merckvetmanual.com. Accessed August 2026.