Figure 3.3: The total fertility rate (TFR) in the world, 2009, the U.S. fertility rate, 2009. The TFR indicates the average number of children a woman would have during her child-bearing years (ages 15–49), assuming that age-specific birthrates stay constant. A rate of 2.1 is needed to produce a stable population over the long run; below that, population will decline. Fast growth is associated with a TFR of 5.0 or higher. Within the United States, the highest fertility rate is found in the state of Utah, while the lowest rate occurs in Vermont.