What is the gestation period for mice?

• A. 19 - 21 days
• B. 21 - 23 days
• C. 24 - 26 days
• D. 15 days

Answer: (A)

Gestation in mice is the time from conception to birth, and in Mus musculus it runs about three weeks. The standard reference window is roughly 19 to 21 days, with many litters born around day 19–20. This short, consistent period reflects their small size and rapid development. Environmental factors such as strain, age, nutrition, housing temperature, and stress can cause a small shift, but 19–21 days is the typical range used in breeding and research settings. Options longer or shorter than this window don’t match the usual development timeline: 24–26 days is longer than normal for mice, 15 days is too short for full-term development, and 21–23 days is just outside the common upper bound.