If you’re new to Medicare or helping a family member navigate it, Part D — Medicare’s prescription drug coverage — is one of the most practically important pieces of the puzzle. Get it right and your medications are affordable and accessible. Get it wrong and you could face unexpected costs, gaps in coverage, or a late enrollment penalty that follows you permanently. This guide explains exactly how Medicare Part D works, how to compare plans effectively, and how to avoid common costly mistakes.
What Is Medicare Part D?
Medicare Part D is optional prescription drug coverage added to Original Medicare. It’s offered by private insurance companies approved by Medicare and is governed by federal rules that standardize certain elements while allowing significant variation in formularies, premiums, and cost-sharing structures. As of 2024, approximately 50 million Medicare beneficiaries are enrolled in either a standalone Part D Prescription Drug Plan (PDP) or a Medicare Advantage plan that includes drug coverage.
The Inflation Reduction Act of 2022 made significant changes to Part D, including capping out-of-pocket drug costs at $2,000/year beginning in 2025 — one of the most significant improvements to the program since its 2006 inception. This cap provides important protection for Medicare beneficiaries who take high-cost specialty medications.
How Part D Coverage Works: The Four Phases
Part D coverage is structured in phases, though the 2025 changes significantly simplified what was once a more complex structure:
Deductible Phase
Most Part D plans have an annual deductible — up to a maximum of $590 in 2025. During the deductible phase, you pay 100% of drug costs until you meet the deductible. Some plans offer $0 deductibles for preferred generic drugs, meaning you immediately pay only a copay for those drugs regardless of where you are in the deductible phase.
Initial Coverage Phase
After meeting your deductible, you pay a copay or coinsurance for covered drugs while the plan pays the rest. Cost-sharing varies by “tier” — preferred generics may have $0-$5 copays, brand-name drugs may have $35-$100 copays, and specialty drugs may have 25-33% coinsurance.
Catastrophic Coverage Phase
Beginning in 2025, once your out-of-pocket drug costs reach $2,000, you pay nothing for the rest of the year. This is a new, simplified structure replacing the former “donut hole” and complex catastrophic phase. The $2,000 cap is a major improvement for beneficiaries who take expensive medications.
Formularies: The Drug List That Determines Your Costs
Every Part D plan has a formulary — a list of covered drugs organized into tiers, with different cost-sharing at each tier. Tier 1 (preferred generics) is cheapest; Tier 5 or 6 (specialty drugs) is most expensive. If your drug isn’t on the plan’s formulary, it’s not covered, and you pay full price.
This is why comparing Part D plans based on your specific medications is essential. A plan with a $0 monthly premium might not cover your drug — making it far more expensive than a plan with a $45 premium that covers your drug at a $10 copay. The Medicare Plan Finder at medicare.gov allows you to enter your specific medications and compare actual costs across all available plans in your area.
Formularies change each year. A drug covered on your plan’s formulary this year may be removed, moved to a higher tier, or subject to new utilization management next year. This is why reviewing your Part D coverage during Annual Enrollment Period (October 15 – December 7) every year is critical — not just when you first enroll.
Part D Premiums and IRMAA
Part D premiums vary significantly by plan and location. The average basic Part D premium in 2025 is approximately $46.50/month, but plans range from under $10 to over $150/month. Higher-income beneficiaries pay an Income-Related Monthly Adjustment Amount (IRMAA) surcharge in addition to their plan premium.
In 2025, Part D IRMAA surcharges begin for individuals with Modified Adjusted Gross Income above $106,000 ($212,000 for married filing jointly), adding $13.70 to $85.80/month depending on income level. CMS bases IRMAA on your tax return from two years prior (2023 income for 2025 IRMAA).
The Late Enrollment Penalty: Why You Shouldn’t Wait
If you don’t enroll in Part D when you first become eligible and you don’t have other creditable drug coverage (coverage at least as good as Medicare’s, such as through an employer or VA), you’ll face a late enrollment penalty when you eventually sign up. The penalty is 1% of the national base beneficiary premium for each month you delayed without creditable coverage — and it’s added to your premium permanently.
For example, if you delayed enrollment for 24 months, your penalty would be 24% of the national base premium, added to whatever plan premium you select, for as long as you have Part D. In 2025, the base premium is approximately $36.78, so a 24-month delay would add roughly $8.83/month permanently.
Even if you take no prescriptions today, enrolling in a low-cost Part D plan during your Initial Enrollment Period makes sense to protect against future penalties. A $10/month plan costs $120/year — far less than a permanent penalty if you develop health conditions requiring expensive medications later.
Low-Income Subsidy (Extra Help)
Medicare offers a Low-Income Subsidy (LIS) program, also called “Extra Help,” for beneficiaries with limited income and resources. Extra Help pays most of the Part D premium, deductible, and cost-sharing for eligible beneficiaries. In 2025, individuals with income up to 150% of the federal poverty level and limited assets may qualify for full Extra Help benefits.
Extra Help beneficiaries typically pay no premium (or a very low premium), no deductible, and fixed copays of $4.50 for generics and $11.20 for brand-name drugs. If you or a family member might qualify, contact Social Security or your State Health Insurance Assistance Program (SHIP) counselor to apply.
Comparing Part D Plans: A Step-by-Step Approach
- List all your medications — Include drug name, dosage, and frequency. Note which pharmacy you prefer to use.
- Use Medicare Plan Finder — At medicare.gov/plan-compare, enter your medications and preferred pharmacy. The tool calculates your estimated annual costs (premium + deductible + copays) for each available plan.
- Compare total costs, not just premiums — The plan with the lowest premium often isn’t the cheapest when you factor in your specific drug costs.
- Check pharmacy network — Plans may charge lower copays at “preferred” pharmacies. Make sure your preferred pharmacy is in the plan’s network and whether it’s preferred or standard.
- Review formulary changes annually — Don’t assume your current plan is still the best option each year. Re-compare during AEP.
Frequently Asked Questions
Can I use GoodRx or manufacturer coupons with Part D?
Starting in 2026 (under the Inflation Reduction Act provisions), manufacturers can offer coupons that count toward your Part D out-of-pocket maximum. Previously, using GoodRx or coupons instead of insurance meant those costs didn’t count toward your deductible or out-of-pocket cap. Rules in this area are evolving — check with your pharmacist or plan for current guidance.
What is “creditable coverage” and why does it matter?
Creditable coverage is drug coverage that’s at least as good as Medicare Part D. Employer-sponsored drug coverage, VA coverage, and certain other plans qualify as creditable. If you have creditable coverage, you can delay Part D enrollment without penalty. Your employer must notify you each year whether your coverage is creditable.
Can I switch Part D plans?
Yes. You can switch to a different Part D plan during Annual Enrollment Period (October 15 – December 7) each year. Your new coverage begins January 1. You can also switch if you qualify for a Special Enrollment Period — for example, if you move to a new area or lose other drug coverage.
What if my drug isn’t on the formulary?
You can request a formulary exception asking the plan to cover your drug. Your doctor must provide documentation supporting medical necessity. You can also appeal a denial. If your medication is truly not available under any plan at reasonable cost, Original Medicare + a standalone PDP may not be the best fit — a Medicare Advantage plan with a more favorable formulary for your drugs might be worth considering.
Finding the right Part D plan requires matching the plan’s formulary to your specific medications — and reviewing that match every year. At Garden State Benefits, Paul Z Olah helps Medicare beneficiaries across NJ and 25 other states navigate Part D enrollment and annual plan comparisons. Call 856-880-6340 or email paul@gardenstatebenefits.com for straightforward guidance.