For years, noncitizens who fail to abide by the terms of their nonimmigrant (temporary) visas were not widely recognized as major contributors to the US undocumented population. Yet since 2005, the ratio of overstays to illegal entries across the border has increased rapidly as the number of border crossings dropped to 1970s levels. As a result, the inflow of overstays has exceeded border crossers for nearly a decade. These developments highlight the importance of accurate and timely estimates of overstays.
In 2017, the US Department of Homeland Security (DHS) released a report, Fiscal Year 2016 Entry/Exit Overstay Report, showing estimates of overstays, by country, for the 50.4 million nonimmigrants admitted in fiscal year 2016 (DHS 2017). At the end of the fiscal year, DHS had not verified the departure of 628,799 nonimmigrants.
The Center for Migration Studies (CMS) compared the DHS overstay estimates to CMS’s estimates of the number of undocumented residents that arrived in the past few years. Data were available to make the comparisons for 133 countries; these countries account for 99 percent of all overstays. The major findings include the following:
- For 90 of the 133 countries, the DHS and CMS estimates differ by less than 2,000, and the correlation between the estimates for those 90 countries is .97, which indicates a very close mutual relationship.
- The DHS estimates of overstays for Canada are far too high.
- The DHS estimates greatly exceed the CMS estimates for about 30 countries, half of them participants in the US Visa Waiver Program (VWP).
- Slightly more than half of the 628,799 reported to be overstays by DHS actually left the country but their departures were not recorded.
- After adjusting the DHS estimates to take account of unrecorded departures, as well as departures in 2016 of overstays that lived here in 2015, overstay population growth was near zero in 2016.
- Thus, while overstays account for a large percentage of the newly undocumented, they represent less than half (44 percent) of the overall undocumented population, and they are less likely than illegal border crossers to be long-term residents.
- The country-specific figures shown here should help DHS focus its efforts on improving the verification of departures of temporary visitors.
- Finally, these comparisons indicate that the DHS estimates do not provide a sound basis for making decisions about admission to, or continuation in, the VWP.
 The 628,799 figure refers to nonimmigrants that arrived in 2016 and whose departure had not been verified by the end of 2016. Thus, as demonstrated in this paper, it includes nonimmigrant admissions whose departure was not verified and actual overstays.
 The US Visa Waiver Program (VWP) is described at https://www.dhs.gov/visa-waiver-program, as follows: “The VWP, which is administered by the Department of Homeland Security (DHS) in consultation with the State Department, permits citizens of 38 countries to travel to the United States for business or tourism for stays of up to 90 days without a visa. In return, those 38 countries must permit US citizens and nationals to travel to their countries for a similar length of time without a visa for business or tourism purposes.”