Environmental Science Practice Exam 2026 – Complete Prep for Dual Enrollment

Replacement level fertility is the number of births per woman that keeps the population size steady over time, because it just replaces the parents who die with a roughly equal number of new births. In many places that rate is about 2.1 children per woman, accounting for mortality before reproductive age. When fertility stays at or near this level, the number of people born balances the number who die, so the population remains relatively stable.

If fertility were higher than replacement, the population would tend to grow, while lower than replacement would lead to a decline. Real-world factors like age structure and migration can modify this, but the long-run effect of replacement-level fertility is stability.