More than half of all Medicare beneficiaries are now enrolled in Medicare Advantage.

That’s a significant shift—up from just 32% in 2015 to 54% in 2025.

And it didn’t happen by accident.

As I wrote two years ago in this piece on the “golden goose” of Medicare Advantage:

So how did we end up with over half of America’s seniors in Medicare Advantage plans—and what does that mean for the future of Medicare?

In this article, I’ll walk through how MA became the behemoth it is today, why it’s been such a financial windfall for insurers, and what needs to change to make the system more sustainable—for patients, providers, and taxpayers alike.

Medicare was born in 1965 when President Lyndon B. Johnson signed it into law, offering health insurance to seniors and people with disabilities. It was a beautiful law—older adults no longer had to drain their retirement savings just to afford hospital stays or doctor visits.

But the original Medicare program, built on a fee-for-service (FFS) model, came with its own set of problems:

When the federal government can’t run things efficiently, we call on the private sector.

In the 1980s, the federal government began looking for ways to improve Medicare’s efficiency and financial sustainability. The Tax Equity and Fiscal Responsibility Act (TEFRA) of 1982 opened the door for private insurers to contract with Medicare and offer managed care plans—planting the seeds of what would become Medicare Advantage.

That experiment evolved through the decades. The Balanced Budget Act of 1997 formally created the “Medicare+Choice” program, which was later rebranded as Medicare Advantage under the Medicare Modernization Act of 2003.

The idea? Let private insurers offer Medicare coverage with added perks and coordinated care—ideally at a lower cost to the government. If done right, it was a win-win-win (triple win?):

Medicare Advantage now covers 54% of all Medicare beneficiaries—that’s 34 million people. Back in 2007, it was just 19%.

But in 2025, that growth is starting to slow down. Enrollment only increased by 1.3 million this year—a 4% bump. That’s still big, but it’s down from 7% the year before. The MA train is still moving, I’d say—but it’s not accelerating like it used to.