Article Excerpt: "...Workers and spouses covered by a worker’s current employment health plan also have a special enrollment period to sign up for Medicare after retirement. If you miss the initial or special periods, you’re left with an annual general enrollment period that runs from January through March.
If you don’t sign up for Medicare Part B when you're first eligible, your monthly premium may go up 10% for each 12-month period you could've had the insurance but didn't sign up. In most cases, you'll have to pay this penalty each time you pay your premiums, for as long as you have Part B. And the penalty increases the longer you go without Part B coverage..."
Resource: www.govexec.com