Michael Hiltzik: Working past 65? Beware of this Medicare trap that could cost you thousands in taxes

We can say two things for sure about the American workforce and its health insurance. First, more Americans are working past the traditional retirement age of 65. Second, more are taking advantage of employer insurance plans that include tax-exempt Health Savings Accounts.

Add these two facts together, and you end up with a pitfall that could cost unwary American workers as much as $2,700 a year in tax exemptions if they exercise their right to enroll in Medicare at 65. That pitfall exists because of the confusing way HSAs interact with Medicare, and because many big employers fail to help their older employees deal with the potential complexities - or even to know about them.

"If you're working for a large employer," says Lawrence Kotlikoff,