Short answer: The Part D late enrollment penalty is a permanent surcharge added to your Part D premium if you go 63 or more days without creditable drug coverage after your initial enrollment period. It’s roughly 1% of the national base premium for each month you went without, for as long as you have Part D.
Medicare wants people to maintain drug coverage continuously. If, after your initial enrollment period, you go 63 days or more without creditable prescription drug coverage (coverage at least as good as Part D; most employer plans qualify), you can owe a late enrollment penalty when you eventually join Part D.
The penalty is about 1% of the national base beneficiary premium for each full month you went without, rounded and added to your Part D premium, and it generally lasts for as long as you have Part D. This is why employers must tell Medicare-eligible employees each year whether their drug coverage is creditable: that notice is what protects employees from the penalty.
Sources
- CMS, Medicare Part D late enrollment penalty and creditable coverage guidance.
Content history
Originally published: June 16, 2026
Last reviewed: June 16, 2026