A 20% coinsurance means you pay 20% of a covered medical bill and your insurance pays the remaining 80%. This split only kicks in after you’ve met your annual deductible, and it stops once you hit your plan’s out-of-pocket maximum. Understanding how these pieces fit together can save you from surprise bills and help you estimate costs before a procedure.
How 20% Coinsurance Works
Coinsurance is your share of a medical bill, expressed as a percentage. If your plan has 20% coinsurance and the approved cost of a service is $100, you pay $20 and your insurer covers $80. The key word here is “approved cost.” Insurance companies negotiate rates with in-network providers, and your coinsurance is based on that negotiated amount, not necessarily the sticker price a hospital lists.
This is different from a copay, which is a flat dollar amount you pay at the time of service. A copay might be $30 for a primary care visit or $50 to see a specialist, regardless of what the visit actually costs. Coinsurance, by contrast, scales with the size of the bill. A 20% share of a $200 lab test is $40, but 20% of a $50,000 surgery is $10,000. That scaling is why the other parts of your plan (your deductible and out-of-pocket maximum) matter so much.
The Payment Sequence
Your costs follow a specific order each plan year. First, you pay the full allowed amount for covered services until you’ve met your annual deductible. This is the amount you owe before your insurance starts sharing costs at all. Once you cross that threshold, coinsurance begins. You pay your percentage (20%) and your insurer pays theirs (80%) on every covered service going forward. Finally, once your total spending on deductibles, coinsurance, and copays reaches your plan’s out-of-pocket maximum, your insurer covers 100% of covered services for the rest of the year.
For 2025, Marketplace plans cap the out-of-pocket maximum at $9,200 for an individual and $18,400 for a family. In 2026, those limits rise to $10,600 and $21,200 respectively. Your plan’s actual limit may be lower than these caps, but it can’t be higher.
A Real-World Calculation
Say you have a plan with a $1,500 deductible and 20% coinsurance, and you receive a $10,000 hospital bill for a covered procedure. Here’s how the math breaks down:
- Deductible: You pay the first $1,500 out of pocket (assuming you haven’t spent anything toward your deductible yet this year).
- Coinsurance: The remaining $8,500 is split. You pay 20% ($1,700) and your insurer pays 80% ($6,800).
- Your total: $3,200 for that bill ($1,500 deductible + $1,700 coinsurance).
If that $3,200 pushes you past your plan’s out-of-pocket maximum, you’d pay less. For example, if your out-of-pocket max is $5,000 and you’d already spent $2,500 earlier in the year, you’d only owe another $2,500 on this bill before your insurer takes over at 100%.
When Coinsurance Doesn’t Apply
Most health plans are required to cover a set of preventive services at no cost to you, even if you haven’t met your deductible. Screenings, immunizations, and annual wellness visits typically carry 0% coinsurance when you use an in-network provider. This is an Affordable Care Act requirement that applies to Marketplace plans and most employer plans. So even if your plan’s standard coinsurance is 20%, you won’t owe anything for these specific services.
Out-of-Network Coinsurance Is Higher
The 20% coinsurance listed on your plan almost always applies to in-network providers. If you see a doctor or go to a facility outside your plan’s network, your coinsurance percentage jumps significantly, often to 40% or more. On top of that, out-of-network providers may charge more than what your insurer considers the “allowed amount,” and you could be responsible for the difference. What you pay out of network may not even count toward your plan’s out-of-pocket maximum, depending on the plan.
Before scheduling a procedure or visiting a specialist, confirming they’re in-network is one of the simplest ways to keep your costs predictable.
20% Coinsurance in Medicare
If you’re on Medicare, 20% coinsurance is the standard for Part B services. After you meet the annual Part B deductible, you typically pay 20% of the Medicare-approved amount for doctor visits, outpatient care, durable medical equipment (wheelchairs, walkers, hospital beds), and mental health services. This applies as long as your provider accepts “assignment,” meaning they agree to charge only the Medicare-approved amount. Many people on Medicare buy a supplemental (Medigap) policy specifically to cover this 20%, since Part B has no out-of-pocket maximum the way Marketplace plans do.
What 20% Coinsurance Means for Your Budget
A plan with 20% coinsurance is among the more common structures and generally represents a moderate cost-sharing arrangement. Plans with lower coinsurance (like 10%) usually come with higher monthly premiums, while plans with higher coinsurance (30% or 40%) tend to have lower premiums but leave you with bigger bills when you actually need care.
The practical question is how much you could owe in a bad year. Look at your deductible, your coinsurance rate, and your out-of-pocket maximum together. The out-of-pocket maximum is your true worst-case scenario for in-network care in a given year. If your plan has a $2,000 deductible, 20% coinsurance, and a $7,000 out-of-pocket max, you’ll never pay more than $7,000 total for covered in-network services, no matter how large the bills get. That number is the one worth planning around.