More than 4 million people have signed up for coverage through Healthcare.gov since the current open enrollment began through Dec. 10, and enrollment has surged leading up to today’s deadline.

The federal website for Affordable Care Act marketplace coverage saw 700,000 signups this Monday and Tuesday, according to the Centers for Medicare & Medicaid Services. Today is the last day to sign up for coverage effective Jan. 1.

CMS said there have been about 250,000 more plan selections during the first 40 days of open enrollment compared to last year. The agency’s most recent signup figures include 1.1 million new customers and 2.9 million who have renewed their coverage.

“Momentum is building,” Department of Health and Human Services Secretary Sylvia Burwell said in the announcement. “As we approach the December 15th deadline for consumers to get coverage that begins January 1st, we’re seeing hundreds of thousands of consumers each day signing up for coverage they want and need."

The average rate hike for benchmark ACA silver plans this year is 22%—compared to 7.5% the year prior—though as the Obama administration has stressed previously, Burwell noted that most marketplace shoppers can find plans with monthly premiums of less than $75 per month.

Source: Center for Health and Economy

That’s because subsidies rise as premiums do, but a new analysis indicates that still comes at a cost. The Center for Health and Economy expects federal spending on advanced premium tax credits to increase by $9.8 billion from 2016 to 2017, reaching $42.6 billion, the nonpartisan research organization said in a new analysis. It predicts the average monthly tax credit will increase by 26% next year to $367.

Under the ACA, "you get a premium increase, you pour more money in," Douglas Holtz-Eakin, the group’s founder and former Congressional Budget Office director, told the Associated Press. "The concern is that will feed more premium increases."