How much is the Part D late enrolment penalty?

Count every full month after your initial enrolment period during which you had neither a Part D plan nor other creditable drug coverage. That count is multiplied by one percent of the national base premium, rounded, and added to whatever your chosen plan charges. Because the base premium moves each year, the penalty amount moves with it.

The commonest cause is someone taking no medication deciding a drug plan is unnecessary. A very inexpensive plan held from the start costs far less than the permanent surcharge, which is the entire argument for enrolling on time even when your pill bottle shelf is empty.

An estimate for planning, not a quote. Medicare and the Marketplace set your real figures.