The short answer
The most expensive Part D mistake is failing to review your drug plan each year, because plans change their formularies, pricing, and preferred pharmacies annually, and a plan that was cheapest last year may not be this year. Other costly errors include choosing a plan on premium alone without checking whether it covers your specific medications affordably, not using preferred pharmacies, and skipping Part D enrollment when first eligible, which can trigger a lifelong late penalty. Reviewing your plan against your actual medications each year is the single best way to avoid overpaying.
So the biggest Part D mistake is not comparing your plan against your actual drugs each year, since plans and prices change annually.
The mistakes to avoid
Watch for choosing a plan by premium alone rather than total cost including your drugs' copays; not re-checking your plan each year as formularies and prices change; ignoring preferred pharmacy pricing that can lower costs; and delaying Part D enrollment when first eligible without other creditable drug coverage, which causes a permanent penalty. Because your medications and the plans both change, last year's best plan may not fit now. Our guide to how to choose a Part D plan covers doing it right.
The theme is matching the plan to your current drugs and pharmacies each year, not relying on premium or past choices.
How to save
Each year during the Annual Enrollment Period, compare Part D plans based on your actual medication list, including each drug's coverage tier and copay and the plan's preferred pharmacies, not just the premium. Enroll on time when first eligible to avoid the late penalty. Tools and a local licensed advisor can compare plans against your drug list at no cost. Our doctor and drug coverage page helps you check coverage. This is educational information.
The takeaway: avoid Part D overpaying by comparing plans against your actual medications and pharmacies each year, and enrolling on time to dodge the late penalty.
Frequently Asked Questions
What is the biggest Part D mistake?
Not reviewing your drug plan each year. Plans change their formularies, pricing, and preferred pharmacies annually, so a plan that was cheapest last year may cost more this year for your medications.
Why should I compare Part D plans by drug cost, not premium?
A low premium can hide high copays for your specific medications. The total cost — premium plus your drugs' copays at preferred pharmacies — is what determines what you actually pay.
What happens if I skip Part D when first eligible?
Without other creditable drug coverage, delaying Part D can trigger a lifelong late-enrollment penalty added to your premium, so enrolling on time is important.
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