Net migration to the UK could plunge by more than half next year in the wake of the Brexit vote, according to a report.
The Government could hit its target for reducing the figure to tens of thousands before the end of the decade - but this would be "at large economic cost", the study suggests.
Net migration - the difference between the numbers arriving and leaving - was an estimated 333,000 in the year to December, the most recent official figures show.
Thinktank the Social Market Foundation set out three forecasts of net migration levels between 2016 and 2020.
Its central forecast, based on estimates of unemployment trends, suggested net migration would be "substantially lower" than it would have been in the event of a vote to remain in the EU "because of the UK's negative economic outlook". In this scenario net migration would fall to 162,000 by 2018 and 131,000 in 2020.
A second forecast, based on a "more pessimistic economic outlook" where the UK leaves the Single Market entirely, envisages a sharper fall to 130,000 in 2018 and to 99,000 in 2020.
Under this forecast the Conservatives would hit their net migration target in 2020, the report said, adding: "This would, however, come at a substantial economic cost."
In the third model, based on early post-referendum figures on job vacancies, net migration could be 141,000 by the end of 2016 - a fall of 58% from last year, the report said.
It added: "The Conservatives would hit their net migration target even earlier, by 2019, but at a large economic cost."
Report author Ben Richards said: "Two of our forecasts show that the Conservatives will meet their net migration target after all, even without any changes to immigration policy.
"This is the result of a deteriorating economic outlook, including a sharp reduction in job vacancies and increased unemployment.
"These forecasts don't take into account actual policy changes on migration - such as the possibility of stricter immigration rules in the event of leaving the EU - but instead just consider how migration tends to fall when unemployment rises and so, in this sense, are cautious estimates.
"The next few years could demonstrate that the state of the economy is more important for net migration than EU membership."