How many days precisely would the baby stay in womb?

There is some variability in the length of human gestation, but on average, a baby will stay in the womb for about 280 days, or 40 weeks, from the first day of the last menstrual period. This is known as the gestational age. However, some babies may be born prematurely, before 37 weeks of gestation, or post term, after 42 weeks of gestation.