They sound like the same thing. They are not remotely the same thing.
HSA. FSA. One letter apart, both offered at open enrollment, both described in the same three sentence blurb in your benefits packet, both letting you pay medical bills with pre tax money.
And for most of your career, the difference barely matters. You put money in, you spend it on doctors, you move on.
Then you turn 55, and the gap between them stops being technical and starts being financial.
One of these accounts hands you an extra catch up contribution, follows you into retirement, grows tax free for thirty years, pays your Medicare premiums, and passes to your spouse untouched when you die.
The other one expires in December and disappears when you leave your job.
Guess which one most people over 55 are enrolled in.
Let's break down what actually changes at 55, why it matters more than at any earlier point in your life, and how to know which one you should be in for your last working decade.