The answer
Is the Part B penalty a one-time fee?
No, the Part B (medical) penalty is not a one-time fee; it is a permanent surcharge added to your monthly premium.
Once a late penalty applies, it stays on your Part B premium for as long as you have Part B, not just for a single year or a single payment. The penalty equals 10% of the standard premium for each full 12 months you delayed enrolling without qualifying coverage, so the longer the delay, the larger the ongoing surcharge. Because it is permanent and recurring, enrolling on time or keeping qualifying coverage matters well beyond your first year. To check whether a penalty would apply to you and how to avoid one, reach out to a licensed Goodsurance advisor at 1-888-301-8091 (TTY 711), Mon to Fri 8 am to 5 pm PT.