English: The main series of projections, released in September 2018, assumes that future international migration will mirror recent historical trends; this is the “middle” migration assumption. In addition to the main series, we also produced three alternative scenarios that are “what if” exercises, examining how the U.S. population would change if future patterns of immigration differ radically from historical trends. For each of the three scenarios described below, the fertility, mortality, and emigration assumptions are the same as those used in the main series; the only component that differs is immigration.

Zero immigration scenario. Assumes that immigration into the United States falls to zero (the theoretical minimum). Under this scenario, there is no immigration, but we still allow for emigration out of the United States. This offers the most dramatic picture of demographic change.

High immigration scenario. Assumes immigration increases by 50.0 percent compared with levels from 2011 to 2015 for all projected years. This scenario shows what the outcome would be if we were underestimating immigration by half in the main series.

Low immigration scenario. Assumes that immigration rates are roughly cut in half from their 2011 to 2015 levels. This scenario is not strictly 50.0 percent less, but is log symmetrical to the values for the high migration scenario. As a result, the projected migration rates vary between 40 and 50 percent less than those projected for the main series in any of the given years, starting with 2017.