About this calculator
Enter the date your guinea pig (sow) was paired with a male (boar) and this calculator estimates her due date using the known gestation range for the species. Guinea pig pregnancies come with a couple of species-specific risks worth understanding, which is why timing matters more here than it might seem for such a small animal.
A surprisingly long pregnancy for a small animal
Guinea pigs are pregnant for 59 to 72 days, averaging around 63 to 68 days — noticeably longer than similarly sized rodents like mice or hamsters, whose pregnancies last only a few weeks. This longer gestation reflects the fact that guinea pig pups are born highly developed (precocial), with fur, open eyes, and the ability to walk and eat solid food within hours of birth, unlike the blind, hairless young of most other rodents.
Litter size and timing
Litters typically range from one to six pups, with two or three being most common; first litters tend to be smaller than later ones. As with several other species on this site, larger litters are generally carried for a slightly shorter time than smaller ones, since the physical space and hormonal load of more pups tends to bring labor on a bit sooner.
The pelvic bone deadline — the single most important timing fact
This is the detail that makes gestation dates unusually important for guinea pigs specifically: the two halves of a sow's pelvis are joined by a flexible symphysis that widens under hormonal influence to allow birth, but this flexibility is largely lost by around 8 months of age if she hasn't been bred before then. A sow bred for the first time after that window has closed faces a serious risk of the pelvis being unable to widen enough for birth, often requiring an emergency cesarean section. This is why responsible breeding guidance is very specific about breeding sows for the first time between about 4 and 7 months of age — not younger (too small and immature) and, critically, not older than around 8 months if it's going to happen at all.
Pregnancy toxemia risk
Guinea pigs, and particularly sows in their last two weeks of pregnancy or carrying large litters, are prone to pregnancy toxemia (also called ketosis), a potentially fatal metabolic condition linked to the heavy energy demands of late pregnancy combined with reduced food intake as the pups take up abdominal space. Sudden lethargy, loss of appetite, or unresponsiveness in a heavily pregnant sow is an emergency, not a wait-and-see situation.
A note on breeding age from the other direction
Just as breeding too late (after the pelvis has fused) is dangerous, breeding a sow too young — before around 4 months — also carries risk, since her body hasn't finished its own growth and a pregnancy at that age competes with her own development for nutrients, often producing smaller, weaker pups. Reputable breeders treat the roughly 4-to-7-month window as a firm target rather than a loose guideline, precisely because guinea pigs are one of the few common pets where the consequences of getting breeding age wrong in either direction can be serious.
Diet through pregnancy
Like all guinea pigs, pregnant sows need a constant supply of vitamin C, since guinea pigs (like humans) can't synthesize it themselves — fresh vegetables and a fortified pellet feed are standard, with needs increasing somewhat during pregnancy and lactation. Unlimited good-quality hay should remain available throughout, both for digestive health and as a steady calorie source as her stomach capacity shrinks in late pregnancy.
Signs birth is near and the birth itself
In the final days, the sow's abdomen becomes very rounded and, close to term, the pelvic bones on either side of the spine visibly widen and become easier to feel through the skin — a physical checkpoint many breeders use alongside the calculated date. Guinea pig births are usually quick, often complete within 30 minutes to a couple of hours for the whole litter, and typically happen without assistance. A sow who strains visibly for more than 15 to 20 minutes without producing a pup, especially given the pelvic risks described above, needs prompt veterinary attention.