Coinsurance is the percentage of a medical bill you pay after you’ve met your deductible. If your plan has 20% coinsurance, you pay 20% of covered costs and your insurance company pays the remaining 80%. Unlike a copay, which is a flat fee (like $30 for a doctor visit), coinsurance varies based on the total cost of the service.
How Coinsurance Fits Into Your Costs
Health insurance costs follow a specific sequence, and coinsurance sits in the middle. First, you pay your monthly premium just to keep your plan active. Then, when you receive care, you pay the full allowed amount out of pocket until you hit your annual deductible. Only after you’ve satisfied that deductible does coinsurance kick in.
Here’s a concrete example. Say your plan has a $3,000 deductible and 20% coinsurance, and you rack up $12,000 in medical bills for the year. You’d pay all of the first $3,000 yourself (the deductible). For the remaining $9,000, you’d pay 20%, which comes to $1,800. Your insurer covers the other $7,200. Your total out-of-pocket cost: $4,800.
Some services use copays instead of coinsurance. A routine doctor’s visit might cost you a flat $30 copay regardless of what the visit actually costs behind the scenes, while a surgery or hospital stay is more likely to involve coinsurance. Your plan documents spell out which services fall into which category.
Common Coinsurance Splits
The most common coinsurance ratios are 80/20 and 90/10, where the first number is the insurer’s share and the second is yours. An 80/20 plan means you pay 20% of covered services after your deductible. A 90/10 plan is more generous, leaving you responsible for only 10%.
Plans with lower monthly premiums often come with higher coinsurance, sometimes 30% or even 40%. Plans with higher premiums tend to offer lower coinsurance. The tradeoff is straightforward: pay more each month for smaller bills when you actually need care, or pay less each month and accept a bigger share of costs if something happens. If you rarely use medical services, a higher coinsurance plan might save you money overall. If you have ongoing health needs, lower coinsurance usually wins out.
The Out-of-Pocket Maximum Caps Your Risk
Coinsurance doesn’t go on forever. Every Marketplace plan (and most employer plans) has an out-of-pocket maximum, which is the most you’ll pay in a year for covered services before your insurer picks up 100% of the tab. For 2025, this cap can’t exceed $9,200 for an individual or $18,400 for a family.
Your deductible, coinsurance, and copays all count toward that limit. Once you hit it, you pay nothing for covered in-network care for the rest of the plan year. This is the safety net that protects you from catastrophic costs, even on a plan with high coinsurance. If you’re choosing between plans, the out-of-pocket maximum matters just as much as the coinsurance percentage, because it tells you your true worst-case scenario for the year.
In-Network vs. Out-of-Network Coinsurance
Your coinsurance rate can change dramatically depending on whether your provider is in your plan’s network. A plan might charge you 20% coinsurance for in-network care but 40% for out-of-network care. That alone can double your share of a large bill.
It gets worse. Out-of-network providers aren’t bound by the rates your insurer has negotiated, so the total bill is often higher to begin with. You’re paying a bigger percentage of a bigger number. And out-of-network costs may not count toward your out-of-pocket maximum, meaning there’s no cap protecting you. Some plans have a separate, higher out-of-pocket limit for out-of-network care, while others have no limit at all. Checking whether your doctors and hospitals are in-network before receiving care is one of the most effective ways to keep coinsurance costs predictable.
When You Don’t Pay Coinsurance
Certain preventive services are exempt from coinsurance entirely under the Affordable Care Act. Immunizations, screening tests, and other recommended preventive care are covered at 100% by your insurer with no cost to you, even if you haven’t met your deductible yet. This applies to services like annual wellness visits, blood pressure screenings, and many cancer screenings. The key requirement is that you receive these services from an in-network provider and that they’re classified as preventive rather than diagnostic.
Coinsurance vs. Copay: A Quick Comparison
- Copay: A fixed dollar amount you pay per visit or service, like $30 for a primary care appointment or $50 for a specialist. The amount stays the same regardless of the total bill.
- Coinsurance: A percentage of the total cost of a service. Your actual dollar amount varies depending on how expensive the service is. Twenty percent of a $500 lab panel is $100, but 20% of a $50,000 surgery is $10,000.
Many plans use both. You might pay a copay for everyday visits and prescriptions, then pay coinsurance for bigger-ticket items like hospital stays, imaging, or outpatient procedures. The summary of benefits document that comes with any plan breaks down exactly which cost-sharing method applies to each type of service.
How to Estimate Your Coinsurance Costs
Before a planned procedure or treatment, you can get a reasonable estimate of your coinsurance by asking your provider’s billing department for the expected cost and checking how much of your deductible you’ve already met. If you’ve satisfied the deductible, multiply the expected cost by your coinsurance percentage. If you haven’t, subtract your remaining deductible first, then apply the coinsurance to whatever is left.
Many insurers also offer cost estimator tools on their websites or apps. These pull in your specific plan details, including how much of your deductible and out-of-pocket maximum you’ve used so far, and give you a personalized estimate for common procedures. Using these tools before scheduling non-urgent care can help you avoid surprises and, in some cases, choose a lower-cost facility for the same service.