What is Medicare coinsurance?

Medicare plans offer help with healthcare costs, but they do not pay for everything.

Aside from the monthly premiums, uncovered costs include deductibles, coinsurance, and copayments. These expenses vary among various Medicare plans.

This article discusses the details of coinsurance in each of Plan A, Plan B, Plan C, and Plan D. It also explains other costs of each part of Medicare, along with eligibility and when to enroll.

We may use a few terms in this piece that can be helpful to understand when selecting the best insurance plan:

  • Deductible: This is an annual amount that a person must spend out of pocket within a certain time period before an insurer starts to fund their treatments.
  • Coinsurance: This is a percentage of a treatment cost that a person will need to self-fund. For Medicare Part B, this comes to 20%.
  • Copayment: This is a fixed dollar amount that an insured person pays when receiving certain treatments. For Medicare, this usually applies to prescription drugs.

How Medigap plans help pay coinsurance

As people with original Medicare have to pay deductibles, coinsurance, and copayments, many of them buy a Medigap plan to help with these costs.

Individual health insurance plans in Florida offers 10 Medicare supplement insurance plans that provide a range of benefits.

All of the plans pay 100% of Part A coinsurance. Eight of the plans pay 100% of Part B coinsurance, while one plan pays 75%, and another pays 50%.

Eligibility and enrollment

There are some variations in eligibility and enrollment between original Medicare (Part A and Part B), Part C, and Part D.

Medicare Part A and Part B

People are eligible for Medicare when they reach the age of 65. Younger individuals with disabilities or end stage renal disease (ESRD) are also eligible.

If someone receives Social Security benefits, they are automatically enrolled in parts A and B when they become eligible.

A person who does not receive Social Security benefits may sign up during the Initial Enrollment Period, which is a 7-month time span that begins 3 months before they turn 65.

A person may also sign up during the General Enrollment Period from January 1 to March 31 of each year. It may be best to sign up during the Initial Enrollment Period, however, to avoid penalties in the form of higher monthly premiums.

Part C and Part D

An individual with Part A and Part B is eligible to buy a Part D plan for prescription coverage. They are also eligible to switch to an Advantage plan, which takes the place of parts A, B, and D.

Someone interested in a Part D plan may join during the Initial Enrollment Period. They may also join in the Open Enrollment Period from October 15 to December 7, but they may have to pay a penalty for late enrollment.

A person interested in joining an Advantage plan may do so during the Initial Enrollment or Open Enrollment periods.


Original Medicare (Part A and Part B), Medicare Advantage (Part C), and prescription drug coverage (Part D), all require a person to pay coinsurance, which is a percentage of healthcare costs.

If a person has Part A and Part B, they may choose to buy a Medigap plan to help pay this and other uncovered expenses.

Coinsurance of Part A and Part B is a standard percentage, but coinsurance of Part C and Part D varies among the plans. In contrast to coinsurance percentages, copayments are a set dollar amount per service.

A person should consider all the costs involved, including deductibles and premiums, when choosing a Medicare plan.