Guinea Pig Pregnancy Calculator (birth date window, 59–72 days)

Understanding the guinea pig pregnancy calculator — concept and principle

This calculator gives the birth window for a pregnant guinea pig (sow) from the mating date, with the middle of the range as the most likely date, and shows how far along she is today. Owners use it to prepare a quiet cage, plan a vet check and know when to watch closely.

A long pregnancy for a small pet: with the default inputs the result is Dec 16, 2026 (expected birth).

How it is calculated

Normal birth window = mating date + 59 days to + 72 days.
Most likely date = day 66, the middle of that range.
Days pregnant = today − mating date; days to due date = 66 − days pregnant.
Week = floor(days ÷ 7) + 1; progress = days ÷ 66.
Stage: before day 59, inside the window (59–72), or past the window.

The principle

Guinea pigs have a long pregnancy for a rodent, 59 to 72 days. That is why the pups are born well developed, with fur, open eyes and teeth, and can eat solid food within days. Litter size runs from 1 to 7, usually about 3. The length varies with litter size: small litters often go longer and large litters shorter. Because of that spread, the calculator shows the whole window and uses its middle only as a single planning date.

Worked example

Default inputs: mating on Oct 11, 2026, viewed on Nov 10, 2026.

Middle of the range, day 66 = Wed, Dec 16, 2026.
Window = Wed, Dec 9, 2026 (day 59) to Tue, Dec 22, 2026 (day 72).
Days pregnant = 30; days to due date = 66 − 30 = 36.
Week = floor(30 ÷ 7) + 1 = 5; progress = 30 ÷ 66 = 45%.
Stage = before the normal birth window.

How to read the result

From about day 59, keep the cage quiet and clean, provide plenty of hay, fresh water and vitamin C-rich food, and avoid handling the sow more than needed. Pups are weaned at about 3 weeks; separate male pups from their mother and sisters early, because they mature quickly.

Common mistakes

Not knowing the mating date because males and females were kept together.
Expecting birth exactly on day 66.
Assuming a large belly late in pregnancy means many pups; it can also be fat or illness.
Breeding a female for the first time when she is older.

Keep in mind: This is an estimate, not a diagnosis. Guinea pigs can develop serious pregnancy problems, including pregnancy toxaemia and difficult births; call a vet experienced with small pets if the sow stops eating, seems weak, or strains without producing a pup.

Frequently asked questions

How long is a guinea pig pregnant?

59 to 72 days.

How many pups does a guinea pig have?

Usually about 3, with a range of 1 to 7.

When are guinea pig pups weaned?

At about 3 weeks.

Sources: Merck Veterinary Manual (pet owner version), "Guinea Pigs at a Glance"

Checked 9 Nov 2026. Merck Veterinary Manual (pet owner version), “Guinea Pigs at a Glance” table: gestation 59 to 72 days, litter size 1 to 7 (usually 3), weaning age 3 weeks.

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