Short answer
A copay is a fixed dollar payment; coinsurance is a percentage of the plan’s allowed cost for a covered service. In HealthCare.gov’s examples, after the deductible is met, a $20 copay and 20% coinsurance both produce a $20 payment for a visit with a $100 allowed amount—but they use different formulas. 1 2
On this page
At a glance
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| Question | Copayment | Coinsurance |
|---|---|---|
| How is it expressed? | Fixed dollars | Percentage |
| What determines the payment? | The stated copay | Rate × allowed amount |
| Payment in the $100 visit example, after deductible? | $20 | 20% × $100 = $20 |
| Before the deductible in those examples? | Full $100 | Full $100 |
These are the supplied HealthCare.gov examples, not promises about every plan. 1 2
What each thing is
Both terms describe what the patient pays toward covered care. A copayment specifies an amount for a service; coinsurance specifies a share of its allowed cost. HealthCare.gov also calls the allowed amount an eligible expense, payment allowance, or negotiated rate. That is the cost basis used in its coinsurance example. 1 2
Key differences
The difference is the calculation, not necessarily the final bill. Holding the applicable copay constant keeps that payment fixed. Holding the coinsurance rate constant makes the payment rise or fall with the allowed amount. Thus, equal payments for one visit do not make the two arrangements equivalent for another. 1 2
How to tell them apart
Look at how the service’s cost sharing is written: a dollar amount indicates a copay; a percentage indicates coinsurance. The limit of this shortcut is that it identifies the formula, not everything owed. In the supplied examples, an unmet deductible changes the payment to the full allowed amount. 1 2
Where they overlap
Both sit within the broader cost-sharing picture rather than replacing the deductible. They also appear in HealthCare.gov’s explanation of the out-of-pocket maximum: after the relevant spending on deductibles, copayments, and coinsurance for in-network care reaches that maximum, the plan pays all costs of covered benefits. 2
Edge cases
A percentage does not mean that percentage applies to every dollar of an episode’s allowable costs. In HealthCare.gov’s high-cost example, $12,000 in allowable costs first requires a $3,000 deductible. The 20% coinsurance then applies to the remaining $9,000, adding $1,800 for a total patient payment of $4,800. 2
Why the distinction exists
The separate labels preserve two different ways to assign the patient’s share. A fixed amount tells you the payment for the specified service; a percentage requires both the rate and the allowed amount to calculate dollars. Calling both simply a patient payment would hide that important arithmetic difference. 1 2
Common misconceptions
A $20 payment alone does not prove that a charge is a copay: 20% of $100 is also $20. Nor does a stated copay or coinsurance rate guarantee that amount before the deductible is met; both supplied office-visit examples instead require the full $100 at that stage. 1 2
Examples
Consider two hypothetical plan arrangements for a covered office visit, with the deductible already met: Arrangement A charges a $20 copay; Arrangement B charges 20% coinsurance. Case 1: at a $100 allowed amount, each charges $20. Case 2: at a $200 allowed amount, A still charges $20 while B charges $40. These cases apply the sources’ fixed-versus-percentage distinction. 1 2