The answer
What is the Part D late enrollment penalty?
The Part D late enrollment penalty is an extra amount added to your monthly drug plan premium if you go too long without creditable prescription drug coverage.
Creditable coverage means drug coverage at least as good as standard Medicare Part D. The penalty applies if you go 63 days or more in a row without it after your Initial Enrollment Period, the first window when you could sign up. The penalty is calculated from the national base premium, which is $38.99 per month in 2026, and it generally lasts for as long as you have Part D. The longer you wait, the larger the penalty grows. The way to avoid it is to keep creditable drug coverage or enroll when first eligible.