Two parts of Medicare, one clear comparison

Medicare Part B vs Part D Cost Comparison: What Each Costs and What Each Covers

Part B and Part D do different jobs, and they come with different premiums, different penalties and different deadlines. I am Lourdes Hernandez, and in this guide I put the two side by side so you can see where your money goes and avoid the late fees that catch so many people off guard.

What Is Medicare Part B and How Much Is It Per Month?

Part B is the medical half of Original Medicare. It covers doctor visits, outpatient care, preventive services, lab work, physical therapy, outpatient mental health care and durable medical equipment. After the annual Part B deductible, Medicare pays 80% of the approved amount for most covered services, and you owe the remaining 20% unless another policy picks it up. Part A, the hospital half, is premium-free for most people, so Part B is where the monthly cost of Original Medicare actually lives.

The standard Part B premium is set nationally and adjusted each year; for 2025 it is $185 per month. Your actual premium can be higher if your income is above the standard thresholds, and lower if you qualify for certain assistance programs. The premium is usually withheld from your Social Security check, which is why many people never see it as a separate bill. What Part B does not cover, and this matters for the rest of this page, is prescription drug coverage. That is a separate decision with a separate premium.

What Is Medicare Part D and How Much Is It Per Month?

Part D is prescription drug coverage, sold by private insurance companies that Medicare approves. Unlike Part B, which is one standard premium, Part D premiums vary by plan and by county: carriers price their drug plans differently in Palm Beach County than in Broward County, and differently again in New Jersey and North Carolina. Every plan maintains a formulary, the list of drugs it covers, and places each medication in a tier that determines what you pay at the pharmacy.

This is why I never recommend picking a Part D plan by premium alone. A plan that costs a few dollars less per month can be far more expensive overall if your medication sits in a high tier, while a plan with a higher premium may cover your drugs at a low copay. The fair comparison starts with your actual medication list. I run each prescription against each plan's formulary for clients in Boca Raton, West Palm Beach and Fort Lauderdale, and the plan that comes out ahead is often not the one with the lowest monthly number, and I am glad to say so plainly when it is.

Medicare Part B vs Part D: Side-by-Side Cost Comparison

Put simply, Part B buys you medical care and Part D buys you prescriptions, and each has its own premium, deductible and rules. Part B has one standard premium that most people pay, currently $185 per month in 2025, with income-based adjustments. Part D has many premiums set by competing carriers, so two neighbors on the same street in Delray Beach can pay different amounts for the same tier of coverage. Part B's deductible applies across your medical services, while a Part D plan has its own drug deductible and then tiered copays or coinsurance at the pharmacy.

Where you get each part also differs. On Original Medicare, Part B comes from Medicare itself and Part D is a separate standalone plan you add. In most Medicare Advantage plans, both are bundled: the Advantage plan includes medical coverage and usually drug coverage in one policy, often with a zero or low premium. That is why people sometimes ask whether they even need Part D. The answer depends on which route you take, and the comparison below should help you see the difference before you decide.

There is one more cost line people forget: the 20% coinsurance that Part B leaves behind. On Original Medicare you handle that with a Medigap supplement or through the cost structure of an Advantage plan. On my page about Medicare Advantage plans rated and cost-compared in Florida, I show how that gap gets handled on each side.

Penalties for Late Enrollment: Part B vs Part D

Both parts punish lateness, in different ways. The Part B penalty is 10% for each full 12-month period you could have enrolled but did not, and it is permanent: it raises your monthly premium for life. If you wait two years past your window, you carry a 20% increase forever. The exception that protects working people is the special enrollment period for those with employer coverage from current work, which lets you delay Part B while that coverage lasts and enroll for 8 months afterward without penalty.

The Part D penalty works differently. It is 1% of the national base beneficiary premium for each month you were without creditable drug coverage after your window opened, and like the Part B penalty it is permanent, added to your monthly Part D premium for as long as you have drug coverage. Creditable coverage means a drug plan or other insurance at least as good as standard Part D, which includes some employer plans. I check whether a client's employer coverage is creditable before advising them to skip Part D, because assuming it is, without checking, is an expensive guess.

Key Enrollment Deadlines You Can't Miss

Your Initial Enrollment Period is the 7 months around your 65th birthday: three months before, the month of, and three months after. Inside it you can sign up for Part B and choose a Part D plan or an Advantage plan that includes drugs. If you miss it and have no employer coverage protecting you, the General Enrollment Period runs January 1 through March 31, with coverage not starting until July 1 and penalties attached.

After that, the annual rhythm takes over. Medicare Open Enrollment runs October 15 through December 7 each year, when anyone can join, switch or drop a Part D plan or an Advantage plan for the next year. From January 1 through March 31, people already in an Advantage plan can switch plans or return to Original Medicare, one change. If you are still working past 65, the special enrollment period rules I explained above apply instead, and they follow your employer coverage, not the calendar.

My guide on open enrollment for Medicare Advantage plans goes deeper into each window and what you can change inside it.

Why You May Need Both Part B and Part D

Part B and Part D are not alternatives; they cover different categories of care, and most people on Original Medicare carry both. Skipping Part D to save the premium is one of the costliest short-term decisions I see, because the penalty accrues every month you go without creditable coverage and stays with you for life, and because a single unexpected prescription can cost far more than a year of premiums. The exception is genuinely creditable employer coverage, and even then I check the plan documents before advising anyone to wait.

The other common path is a Medicare Advantage plan that bundles medical and drug coverage together, which is why some people never carry a separate Part D. Either route is legitimate. What matters is that the drugs you actually take are covered well under whatever you choose, checked every year, because formularies move medications between tiers annually and a copay that was manageable in January can climb by summer. I re-run every client's medication list against their plan each fall, and it costs them nothing but fifteen minutes.

If you are facing this decision while also thinking about final expenses, I wrote a plain comparison of burial insurance versus life insurance for FL, NJ and NC families. And if you would rather talk through your own Part B and Part D numbers, call me at (551) 223-3854 or book a plan review. I serve Palm Beach County, Broward County, Toms River, Brick and North Carolina, in English and Spanish, se habla español, and there is no charge for my help.