Guinea Pig Pregnancy Calculator by MarkGuinea Pig Pregnancy CalculatorEstimate your guinea pig’s delivery date and track pregnancy stages. Mating Date ? Select the date of successful mating (e.g., 2025-04-01). Gestation Period (days) ? Average is 65 days; range is 59–72 days (smaller litters may take longer). Calculate ResetEnter the mating date, then click “Calculate”. JavaScript is disabled. Please enable it to use the calculator.