Medicare Part D Costs in 2026: How to Compare Drug Plans and Stop Overpaying

Your parent takes four medications. One of them costs $300 per month at retail. You need to find a Part D plan that covers all four drugs at a price that makes sense. There are 30 plans available in their zip code. Each has a different premium, deductible, formulary, and pharmacy network. Medicare.gov has a comparison tool, but it takes 45 minutes to figure out, and the results do not clearly tell you which plan is cheapest.

This is the reality of Part D shopping. It is tedious, it matters enormously, and almost nobody does it properly. Here's how to do it right.

What Part D costs look like in 2026

Every Part D plan has the same basic cost structure, but the specific numbers vary from plan to plan:

Monthly premium. This is what your parent pays just to have the plan, whether they fill prescriptions or not. Premiums range from $0 to over $100 per month depending on the plan. The national average is around $40-$50 per month.

Annual deductible. The maximum allowed deductible in 2026 is $590. Some plans have no deductible at all, and some have a lower one. Your parent pays full price for prescriptions until the deductible is met (unless the plan waives the deductible for certain drug tiers, which many do for generics).

Copays and coinsurance. After the deductible, your parent pays a copay (flat fee) or coinsurance (percentage of cost) for each prescription. The amount depends on which "tier" the drug falls into on the plan's formulary.

The $2,000 out-of-pocket cap. Thanks to the Inflation Reduction Act, once your parent has paid $2,000 in out-of-pocket costs (deductible + copays + coinsurance), they pay nothing more for covered prescriptions for the rest of the year. For full details on this cap and the donut hole changes, read our dedicated guide.

Understanding formulary tiers

The formulary is the list of drugs a Part D plan covers. Each drug is assigned to a tier, and the tier determines cost. The typical structure:

The same drug can be on Tier 1 with one plan and Tier 3 with another. A generic blood pressure medication might cost $3 per month on one plan and $15 per month on another. Over a year, that difference adds up.

This is why comparing plans based on premiums alone is misleading. A $0 premium plan that puts your parent's most expensive medication on Tier 4 will cost far more than a $40/month plan that has the same drug on Tier 2.

How to compare Part D plans: step by step

Step 1: Gather your parent's medication list

You need the exact information for each prescription:

• Drug name (brand or generic)
• Dosage (e.g., 10mg, 50mg)
• How often they take it (daily, twice daily)
• Quantity per fill (30-day supply, 90-day supply)

Get this from your parent's current pharmacy or their doctor's office. Do not rely on memory -- a wrong dosage will give you wrong cost estimates.

Step 2: Use the Medicare Plan Finder

Go to Medicare.gov/plan-compare.

1. Enter your parent's zip code
2. Select "Drug plans" (for standalone Part D) or "Health plans" (if also comparing Medicare Advantage plans with drug coverage)
3. Add each medication with the correct dosage and quantity
4. Select your parent's preferred pharmacy (costs vary by pharmacy, and some plans have preferred pharmacy networks with lower copays)
5. Review the results sorted by estimated annual cost

The Plan Finder gives you an estimated total annual cost for each plan, including premiums, deductible, and drug costs. This is the number to compare -- not the premium alone.

Step 3: Check the details before choosing

The Plan Finder's annual cost estimate is a good starting point, but check these details:

Prior authorization and step therapy. Some plans require prior authorization for certain drugs, meaning your parent's doctor must get approval from the plan before the prescription is covered. Others use "step therapy," which requires your parent to try a cheaper drug first before the plan will cover the one their doctor actually prescribed. These restrictions are listed in the plan's formulary.

Quantity limits. Some plans limit how many pills per month they will cover for certain medications. If your parent's doctor prescribes 60 tablets per month but the plan only covers 30, they will pay out of pocket for the rest.

Mail-order options. Many plans offer lower copays for 90-day supplies through mail-order pharmacies. If your parent takes maintenance medications (drugs they take every day long-term), mail order can save hundreds per year.

Pharmacy network. Plans have preferred and non-preferred pharmacies. Costs at a non-preferred pharmacy can be significantly higher. Make sure your parent's regular pharmacy is in-network, ideally as a preferred pharmacy.

Standalone Part D vs. Medicare Advantage drug coverage

If your parent has Original Medicare and a Medigap policy, they need a standalone Part D plan for prescription coverage. Medigap does not cover prescriptions.

If your parent has a Medicare Advantage plan, drug coverage is usually included (these are called MA-PD plans). They cannot also have a standalone Part D plan -- enrolling in standalone Part D while on Medicare Advantage would disenroll them from the Advantage plan.

The comparison process is the same either way: check the formulary, check the tiers, check the pharmacy network, and calculate total annual cost. The difference is that with Medicare Advantage, your parent is evaluating the drug coverage as part of a larger package that includes medical coverage, networks, and prior authorization rules.

Part D penalties: the cost of waiting

If your parent goes 63 or more consecutive days without Part D or other creditable prescription drug coverage, they face a late enrollment penalty. The penalty is calculated at 1% of the national base beneficiary premium for every full month without coverage.

In 2026, the national base premium is $36.78. So:

• 12 months without coverage = approximately $4.41 per month penalty
• 24 months = approximately $8.83 per month
• 36 months = approximately $13.24 per month

This penalty is added to whatever premium they pay and it lasts for the rest of their life.

The most common way families trigger this penalty: the parent retires, has no drug coverage, and assumes they "don't need Part D" because they don't take many medications. Then three years later, they get a diagnosis that requires expensive drugs, and they discover they owe the penalty plus the premiums plus the drug costs.

The lesson: enroll in Part D when first eligible, even if your parent's current medication costs are low. A cheap Part D plan with a $0 deductible and low premiums is insurance against the penalty and against future drug costs.

When to review Part D coverage

Every year during the Annual Enrollment Period (October 15 - December 7). This is not optional. Plans change their formularies, premiums, and pharmacy networks annually. CMS requires plans to notify members of changes, but these notices are easy to overlook in a pile of mail.

After any medication change. If your parent's doctor starts a new medication or changes a dosage, check whether the current plan covers the new drug and at what tier.

If your parent moves. Part D plans are regional. Moving to a new state (or even a new county) may mean the current plan is no longer available or the pharmacy network has changed. A move triggers a Special Enrollment Period to switch plans.

Common Part D mistakes

Choosing the cheapest premium. A $0 premium plan with high copays on your parent's drugs will cost more than a $40/month plan with low copays. Total annual cost is the only number that matters.

Not checking the formulary every year. A drug covered at Tier 1 this year might move to Tier 3 next year. If you don't check, you won't know until your parent gets hit with a $60 copay instead of $5.

Ignoring preferred pharmacy networks. Some plans offer copays 50% lower at preferred pharmacies. If your parent's pharmacy is not on the preferred list, switching pharmacies (or switching plans) can save real money.

Assuming Medicare Advantage drug coverage is good enough. MA-PD formularies can be more restrictive than standalone Part D plans. If your parent's Advantage plan dropped a medication or moved it to a higher tier, the October enrollment period is the time to shop for alternatives.

Part D is one of those things that rewards an hour of homework with hundreds of dollars in savings. If you want a structured approach to the comparison process -- including a formulary comparison worksheet, pharmacy cost tracker, and annual review checklist -- the Medicare Enrollment Guide puts it all in one printable toolkit for $14.