WASHINGTON — With just three weeks left to sign up under President Barack Obama health care law, a major survey tracking the rollout finds that the uninsured rate keeps going down.

The Gallup-Healthways Well-Being Index, released Monday, found that 15.9 percent of U.S. adults are uninsured thus far in 2014, down from 17.1 percent for the last three months — or calendar quarter— of 2013.

That translates roughly to 3 million to 4 million people getting coverage.

Gallup said the share of Americans who lack coverage is on track to drop to the lowest quarterly level it measured since 2008, before Obama took office.

The survey found that almost every major demographic group made progress getting health insurance, although Hispanics lagged.