Affordable Care Act enrollment is at an all-time high, according to new data from the Treasury Department. Nearly 21 million people are currently insured by an ACA health plan.

And over the last decade, nearly 50 million have been on an ACA plan at some point; that’s one in seven Americans.

The Affordable Care Act marketplaces were always intended to fill a gap in the health insurance market. People often buy coverage just for a little while, according to Matthew Fiedler at the Brookings Institution.

“After they’ve lost their job or when they experience an income change,” he noted. And then they move on when they get a new job.

Because of that, Fiedler said that it’s been hard to know how many people have taken advantage of the marketplaces over the years. Now, we do: 50 million.

“The number of people who have touched the marketplace at some point is significant, and larger than you sort of might guess from just looking at the number of people enrolled at any point in time,” said Fielder.

Signups have grown significantly since the pandemic began, added Cynthia Cox at the health policy nonprofit KFF.

“The number of people enrolled has almost doubled in the last four years,” she said — from about 11 million in 2020 to about 21 million this year.

That’s largely because the Biden administration and Congress made subsidies more generous, which has made buying coverage more affordable.

“It used to be that, before these subsidies were available, a family or a retired couple might have to pay like 20% of their income,” Cox said.

Today, that’s capped at 8.5%. And many low-income families can get insurance for free.

“These enhanced subsidies have made a huge impact,” Cox said.

Those subsidies are only in place through next year, though. If they’re allowed to expire, Cox said that she expects the uninsured rate to rise.