A deductible is the fixed dollar amount you pay out of pocket before your insurance starts covering costs. Coinsurance is the percentage of each bill you’re responsible for after you’ve met that deductible. They work in sequence: the deductible comes first, and coinsurance kicks in second.
Understanding how these two pieces fit together can save you from surprise bills and help you choose the right plan during open enrollment.
How a Deductible Works
Your deductible is a yearly threshold. If your plan has a $1,000 deductible, you pay the full cost of most medical services until you’ve spent $1,000 that year. Once you cross that line, your insurance begins picking up a share of the tab. The deductible resets every plan year, so you start from zero again each January (or whenever your plan year begins).
Not everything requires you to hit the deductible first. Federal law requires most health plans to cover a set of preventive services, like immunizations, cancer screenings, and annual wellness visits, at no cost to you, even if you haven’t met your deductible. These services must be provided by an in-network provider to qualify.
How Coinsurance Works
Once you’ve satisfied your deductible, coinsurance is how you and your insurer split the remaining costs. It’s expressed as a percentage. If your plan has 20% coinsurance, you pay 20% of each covered medical bill and your insurance covers the other 80%. On a $500 lab bill, that means you owe $100 and your insurer pays $400.
The most common split is 80/20 (insurer pays 80%, you pay 20%), but plans also use 70/30 or 60/40 arrangements. As a general rule, plans with lower monthly premiums tend to have higher coinsurance percentages, meaning you pay a bigger share when you actually use care. Plans with higher premiums typically flip that equation, covering a larger portion of each bill.
The Payment Sequence, Step by Step
Here’s how costs flow through your plan over the course of a year:
- Before the deductible: You pay the full allowed cost for most services. If you see a specialist and the visit costs $250, you owe all $250. That amount counts toward your deductible.
- After the deductible: Your insurance starts sharing costs. You pay your coinsurance percentage (say 20%) and your insurer covers the rest. A $250 visit now costs you $50.
- After the out-of-pocket maximum: Once your total spending on deductibles, coinsurance, and copays reaches your plan’s annual out-of-pocket maximum, your insurer covers 100% of covered services for the rest of the year.
A Real-World Example
Say your plan has a $1,500 deductible, 20% coinsurance, and a $8,300 out-of-pocket maximum. In March, you need a procedure that costs $10,000.
You pay the first $1,500 yourself (the deductible). That leaves $8,500. Your coinsurance applies to that remaining balance: 20% of $8,500 is $1,700, and your insurer covers the other $6,800. Your total bill for the procedure is $3,200 ($1,500 deductible plus $1,700 coinsurance).
Now you’ve spent $3,200 toward your out-of-pocket maximum of $8,300. If you need more care later that year, you’d keep paying 20% coinsurance until your total yearly spending hits $8,300. After that, your plan covers everything.
Coinsurance vs. Copays
People often confuse coinsurance with copays, but they work differently. A copay is a flat dollar amount you pay for a specific service: $30 for a primary care visit, $50 for a specialist, $15 for a generic prescription. The amount stays the same regardless of the total bill. Coinsurance, by contrast, is a percentage of the bill, so what you owe scales up or down depending on how expensive the service is.
Many plans use both. You might pay a $30 copay for routine office visits but owe 20% coinsurance for surgery or imaging. Some plans apply copays before you meet your deductible for certain services like prescriptions or urgent care, while coinsurance only applies after the deductible is met. Your plan’s summary of benefits spells out which cost-sharing method applies to each type of service.
How Plan Type Affects Your Costs
The balance between your deductible and coinsurance varies by plan design. A high-deductible health plan (HDHP) requires a minimum deductible of $1,650 for individual coverage or $3,300 for family coverage in 2025. These plans pair with health savings accounts (HSAs), which let you set aside pre-tax money for medical expenses. In exchange for the high deductible, HDHPs sometimes offer lower coinsurance once you clear that threshold.
Lower-deductible plans charge higher monthly premiums but start sharing costs sooner. If you use medical care frequently, paying more each month for a lower deductible and lower coinsurance percentage can save money overall. If you rarely see a doctor, a high-deductible plan with lower premiums might make more sense since you’re unlikely to hit the deductible anyway.
The Out-of-Pocket Maximum as Your Safety Net
Both your deductible and your coinsurance payments count toward your plan’s annual out-of-pocket maximum. For 2025, federal rules cap this at $8,300 for individual coverage and $16,600 for family coverage. In 2026, those limits rise slightly to $8,500 and $17,000.
Once you reach this ceiling, your insurer pays 100% of covered services for the remainder of the plan year. This is the feature that protects you in a worst-case scenario, like a major surgery, cancer treatment, or extended hospital stay. Without it, the 20% coinsurance on a $200,000 hospital bill would be $40,000. With the cap, your total exposure is limited to the out-of-pocket maximum regardless of how large the bills get.
Choosing the Right Balance
When comparing plans, look at the deductible and coinsurance together rather than in isolation. A plan with a $500 deductible and 40% coinsurance could cost you more in a major medical event than a plan with a $1,500 deductible and 10% coinsurance. The out-of-pocket maximum is what ultimately matters most for expensive care, but for routine and moderate expenses, the deductible-to-coinsurance ratio shapes your real costs.
Think about your expected healthcare use. If you anticipate a surgery or ongoing treatment, estimate the total cost and run it through each plan’s deductible, coinsurance, and out-of-pocket maximum to see which plan leaves you paying less. If you expect a healthy year with just a few doctor visits, focus on which plan’s premiums and copay structure make those visits affordable without worrying much about coinsurance you may never trigger.