After a hospital stay or surgery, you receive a bill showing your insurance paid 80% of the cost — but you still owe 20%. That 20% is your coinsurance, and for a $50,000 surgery, it translates to $10,000 out of your pocket. What is coinsurance, exactly? It’s the percentage of a covered healthcare cost you pay after you’ve met your deductible. Unlike a copay (a flat fee like $30), coinsurance scales with the size of the bill — which makes understanding it essential before you face a major medical expense.
This article is part of our healthcare policy guide, designed to make insurance terms less intimidating and more actionable.
How Coinsurance Works: Step by Step
Coinsurance only kicks in after you’ve satisfied your annual deductible. Here’s the sequence for a typical 80/20 plan with a $1,500 deductible:
Step 1: You receive medical care that generates a $10,000 bill (at the insurance-negotiated rate).
Step 2: If you haven’t met your $1,500 deductible yet, you pay the first $1,500 yourself.
Step 3: The remaining $8,500 is split according to your coinsurance ratio. In an 80/20 plan, insurance covers 80% ($6,800) and you pay 20% ($1,700).
Your total cost: $1,500 (deductible) + $1,700 (coinsurance) = $3,200.
The “80/20” label means the plan pays 80% and you pay 20%. Other common splits include 70/30 and 60/40. A higher plan share (like 90/10) typically comes with a higher monthly premium.
Coinsurance vs. Copay: Understanding the Difference
Both are forms of cost-sharing, but they work differently:
- Copay: A fixed dollar amount ($30, $50, $75) paid at the time of service. Predictable and consistent.
- Coinsurance: A percentage of the total bill. The amount you owe depends on how much the service costs.
Many plans use both. You might pay a $30 copay for a routine office visit but owe 20% coinsurance for a hospitalization. The CMS marketplace glossary defines both terms clearly for consumers comparing plans.
For a full breakdown of copays, see our guide to what is a copay.
The Role of the Deductible
Your deductible is the amount you pay for covered services before your insurance starts sharing costs through coinsurance. In 2024, the average annual deductible for single coverage in employer plans was approximately $1,735, per the Kaiser Family Foundation.
Until you hit that deductible, you’re paying the full negotiated rate for most services (with exceptions for preventive care and, in some plans, certain copay-covered services). After the deductible is met, coinsurance applies to covered services for the remainder of the plan year.
For a deeper comparison of these two concepts, see our article on deductible vs. out-of-pocket maximum and our explainer on what is a deductible in health insurance.
Your Out-of-Pocket Maximum: The Safety Net
If coinsurance percentages make you nervous about catastrophic bills, the out-of-pocket maximum provides a ceiling. This is the most you’ll pay for covered in-network services in a plan year. Once your combined deductible payments, coinsurance, and copays reach this amount, your insurance covers 100% of additional covered costs for the rest of the year.
For 2025 ACA marketplace plans, the out-of-pocket maximum cannot exceed $9,200 for individual coverage or $18,400 for family coverage, per CMS. Many employer plans set lower limits.
Here’s a complete example using our earlier scenario:
- Deductible: $1,500
- Coinsurance: 80/20 (you pay 20%)
- Out-of-pocket maximum: $6,000
- Total medical bills for the year: $100,000
You pay: $1,500 (deductible) + 20% of remaining costs until your total out-of-pocket spending hits $6,000. After that, insurance covers everything. Without the out-of-pocket max, 20% of $100,000 would be $20,000 — the cap protects you from that scenario.
In-Network vs. Out-of-Network Coinsurance
Most plans have different coinsurance rates depending on whether you use in-network or out-of-network providers. A typical structure might look like:
- In-network: 80/20 (you pay 20%)
- Out-of-network: 60/40 (you pay 40%)
The financial difference is substantial. A $20,000 hospital bill at in-network coinsurance costs you $4,000 (after deductible). That same bill out-of-network costs you $8,000 — plus the out-of-network deductible may be higher, and the out-of-pocket maximum is often separate (and higher) from the in-network limit. Some plans, particularly HMOs, provide no out-of-network coverage at all except for emergencies.
Common Coinsurance Scenarios
Understanding coinsurance in the abstract is one thing — seeing how it plays out in real situations makes the concept concrete. Here are three common scenarios where coinsurance significantly affects your bill.
Hospital Stay
A 3-day hospital stay might generate a $30,000 bill at the negotiated rate. With a $2,000 deductible already met and 20% coinsurance, your share would be $6,000 (20% of $30,000). If your deductible hasn’t been met yet, add that on top. This is where the out-of-pocket maximum becomes your financial safety net — without it, a serious illness or injury could generate devastating bills even with insurance.
Prescription Drugs
Many plans use coinsurance rather than copays for specialty medications. A biologic drug for rheumatoid arthritis might cost $5,000 per month. At 30% coinsurance, your share would be $1,500 monthly — until you hit your out-of-pocket maximum. This is why specialty drug coinsurance is one of the most important numbers to check when selecting a plan if you take expensive medications. Many drug manufacturers offer copay assistance programs that can help offset these costs.
Outpatient Surgery
An outpatient procedure like a knee arthroscopy might run $8,000 at the negotiated rate. With a $1,500 deductible met and 80/20 coinsurance, you’d owe $1,600 (20% of $8,000). Had you chosen a 70/30 plan with a lower premium, the same procedure would cost you $2,400 — $800 more for that single event. Multiply these differences across a year’s worth of care, and the coinsurance rate becomes a major factor in total spending.
How Coinsurance Affects Plan Selection
When choosing a health insurance plan during open enrollment, the coinsurance rate directly impacts your financial exposure. Consider these scenarios:
If you rarely use healthcare (young, healthy, no chronic conditions): A plan with a higher deductible, higher coinsurance (like 70/30), and a lower monthly premium may save you money overall. You’re betting that you won’t need expensive care.
If you use healthcare regularly (chronic conditions, planned surgeries, ongoing prescriptions): A plan with a lower deductible, lower coinsurance (like 90/10), and a higher premium provides more predictable costs and limits your exposure when you do use services.
The key is running the math based on your expected healthcare usage. The Healthcare.gov plan comparison tool lets you estimate total annual costs for different plans based on your anticipated needs.
Tips for Managing Coinsurance Costs
Knowing your coinsurance rate is the first step. Managing it effectively requires a few proactive strategies.
- Track your deductible status. Log into your insurer’s member portal or app regularly to see how close you are to meeting your deductible. Once it’s met, your coinsurance rate kicks in — and you might want to schedule any elective procedures or imaging you’ve been delaying.
- Ask for cost estimates before procedures. Most insurers offer cost estimator tools online. Call the billing department of the provider and your insurance company to get a written estimate of your coinsurance responsibility before committing to expensive care.
- Choose the right setting for care. The same procedure can cost dramatically different amounts depending on where it’s performed. An MRI at a freestanding imaging center might cost $500, while the same scan at a hospital outpatient department might be $2,000. At 20% coinsurance, that’s the difference between $100 and $400 out of your pocket.
- Time elective care strategically. If you’ve already met your deductible and are nearing your out-of-pocket maximum, scheduling additional procedures in the same plan year maximizes the coverage you’re getting. Pushing them to the next plan year resets your deductible and restarts your coinsurance from zero.
Frequently Asked Questions
Does coinsurance apply before or after the deductible?
After. You pay 100% of covered costs (at the negotiated rate) until your deductible is met. Only then does the coinsurance split begin. The exception is preventive services, which are covered at 100% with no deductible or coinsurance in ACA-compliant plans.
What does “0% coinsurance” mean?
It means you pay nothing for that service after your deductible is met — the plan covers 100%. Some plans list certain services (like preventive care) at 0% coinsurance even before the deductible. Always check whether the 0% applies before or after the deductible.
Can I negotiate my coinsurance rate?
No. Coinsurance percentages are set by the plan design and cannot be negotiated individually. However, you can choose a different plan with a more favorable coinsurance split during open enrollment. You can also sometimes negotiate the underlying bill with the provider, which indirectly reduces your coinsurance amount.
Why is my coinsurance different for different services?
Plans often assign different coinsurance rates to different service categories. For example, a plan might have 20% coinsurance for hospitalization but 30% for outpatient surgery, or 10% for generic drugs but 40% for specialty medications. This tiered structure incentivizes you to use lower-cost options when possible.
The Bottom Line
Coinsurance is the percentage-based slice of medical costs you share with your insurance company after meeting your deductible. Unlike a flat copay, it scales with the size of your bill — which means it matters most for expensive care like hospitalizations, surgeries, and specialty treatments. Always know your plan’s coinsurance rate, whether you’re using in-network providers, and what your out-of-pocket maximum is. Those three numbers tell you the worst-case financial scenario for any plan year and help you make informed decisions about both plan selection and where you seek care.