Missing a Medicare enrollment deadline can cost seniors over $8,000 over a lifetime

Failing to enroll in Medicare Part B or Part D on time can lock seniors into permanently higher premiums, according to GoBankingRates. A 12-month delay in Part B enrollment adds roughly a 10% premium surcharge, about $17.50 a month at today's roughly $175 base rate, which can total more than $4,000 over 20 years, said Evan Farr, a certified elder law attorney.

Part D penalties, which typically run $10 to $30 a month depending on how long someone went without drug coverage, can add up to $8,000 to $15,000 over a retiree's lifetime, Farr said. Financial advisor Brandon Hill said gaps in coverage after Medicare eligibility, not just missed paperwork, are what trigger the penalties.

Confusion stems from Medicare's multiple, overlapping enrollment windows rather than a single deadline, Farr said. The initial enrollment period runs seven months, starting three months before someone turns 65 and ending three months after. Missing it means waiting for the next general enrollment period while the penalty accrues for life.