A copay is a fixed dollar amount you pay for a covered service, set in advance and the same every time. Coinsurance is a percentage of the allowed amount for that service, so it changes with the service. The Texas Department of Insurance states the timing rule: "Coinsurance kicks in after you have met your plan's annual deductible." Copays are often charged from the start of the plan year. Which one applies to a given service is written in your plan documents, service by service.
This is general information about how health plan cost sharing is written. It is not medical, insurance or financial advice, it does not recommend a plan or a plan structure, and it does not interpret any bill or Explanation of Benefits. Questions about your own coverage belong with your plan administrator or your state Department of Insurance. This site's full position is set out in our disclaimer.
Sources checked August 11, 2026. Cost-sharing design varies by plan and plan year. Your Summary of Benefits and Coverage is the authority for your own plan.
The one-sentence difference, and the better question
Fixed amount versus percentage. That is the difference every comparison leads with, and it is correct as far as it goes.
The better question is this: when the price of a service is unknown in advance, which of you is exposed to it? Answer that and the two words stop being vocabulary and start being structure. A copay is a number the plan committed to before anyone knew what the care would cost. A coinsurance percentage is a share of a number that will not exist until the claim is processed.
Everything below is that one idea, worked out.
What a copay is
The Texas Department of Insurance defines it in its health insurance glossary, last updated November 8, 2024, as "a fixed amount that you must pay for a covered health care service, usually when you receive the service."
Two features matter. It is fixed, and it is usually collected at the point of care rather than billed later.
TDI illustrates the pattern with a plan that charges "$15 for generic prescription drugs, $30 to visit a primary care doctor, or $50 to see a specialist." Those are the department's illustration of how copays are tiered by service type. They are not typical amounts, and no amount in this article should be read as what any plan charges.
The California Department of Insurance describes the same instrument as "a flat amount you pay for each visit to a doctor or for each prescription."
The structural feature of a copay is that it is the same regardless of what the service turns out to cost. A primary care visit that produces a five-minute conversation and one that produces a long workup carry the same copay for the visit, if the plan is written that way. The variance lands on the plan.
What coinsurance is, and the number it is taken of
The Texas Department of Insurance defines coinsurance as "your share of the costs of a covered health care service," and then adds the clause that most explanations drop: coinsurance "is calculated as a percent of the allowed amount for the service."
Not a percent of the bill. A percent of the allowed amount.
The same department publishes a worked example, dated April 17, 2025: "If your plan's allowed amount for a treatment is $100, your coinsurance payment of 20% would be $20. Your plan pays the remaining $80."
The allowed amount is a defined term with its own meaning. TDI's glossary calls it "the maximum amount a plan will pay for a covered health care service." Covered California's glossary describes it from the contract side as "the amount a health insurance plan and health care provider have agreed on as reimbursement for a service." For in-network care it is a negotiated rate, and it is usually lower, sometimes much lower, than the provider's list charge.
This is where most self-made estimates go wrong. Taking twenty percent of the number printed on a clinic's paperwork produces a figure that is too high, because the clinic's number is the charge and the plan's arithmetic runs on the allowed amount. That relationship is worked through in in-network vs out-of-network and the allowed amount.
Who carries the risk when the price is unknown
Here is the difference the comparison articles do not name.
A copay transfers price variance to the plan. Coinsurance leaves it with you.
Under a copay, your exposure for that service is decided before the service happens. Whatever the allowed amount turns out to be, your share is the printed number. The plan absorbs the difference between an inexpensive instance and an expensive one.
Under coinsurance, your share scales with the allowed amount. Twenty percent of a small allowed amount is small. Twenty percent of a large one is large. There is no per-service cap inside the coinsurance mechanism itself.
The only thing that bounds coinsurance is the out-of-pocket maximum, which is a plan-year ceiling rather than a per-service one. So a single high-cost episode under coinsurance can move a household from paying almost nothing to paying its entire annual maximum, and the mechanism contains nothing to slow that down in between. What accumulates toward that ceiling, and what does not, is covered in what counts toward your out-of-pocket maximum.
This is why the two are not simply different notations for the same idea. They allocate uncertainty differently, and uncertainty is most of what makes medical costs hard to plan around.
Where each one sits relative to the deductible
The Texas Department of Insurance gives the rule for coinsurance in one sentence: "Coinsurance kicks in after you have met your plan's annual deductible, which is what you pay out of pocket before your plan starts picking up a share of medical expenses."
Copays are the less tidy case, and the honest answer is that it depends on the plan.
Some plans charge copays for named services from the first day of the plan year, with the deductible running separately on other categories. Other plans apply the deductible first and only then begin charging copays. Some plans use both structures for different service categories inside the same document: copays for office visits and prescriptions, coinsurance for imaging, surgery and hospital stays.
That variation is the reason two people who both say they "have a $30 copay" can pay differently for the same appointment. It is not a contradiction. It is two plan designs.
There is one more wrinkle worth knowing before reading a plan summary. Whether a copay counts toward the deductible is also a plan choice, and it is separate from whether the copay is charged before the deductible is met. Both answers live in the same document and neither can be assumed.
Side by side
| Copay | Coinsurance | |
|---|---|---|
| Form | Fixed dollar amount | Percentage |
| Calculated on | Nothing; it is set in advance | The allowed amount for the service (TDI) |
| Known before care | Yes | No, not until the allowed amount is set |
| Typically charged | Often at the time of service | After the claim is processed |
| Relative to the deductible | Plan design choice; can be before or after | After the deductible is met (TDI) |
| Who carries price variance | The plan | You |
| Per-service ceiling | The copay itself | None; only the annual out-of-pocket maximum |
| Counts toward the out-of-pocket maximum | Generally yes for covered services | Generally yes for covered services |
Both are cost sharing, and both are usually accumulating toward the same annual ceiling. They differ in shape, in timing and in who is exposed.
Which one applies to you, and where that is written
Not in an article. In two documents and one screen.
The Summary of Benefits and Coverage. This is the standardized document that lists cost sharing by service category, so office visits, specialist visits, emergency care, imaging, prescriptions and hospital stays each show whether they carry a copay, coinsurance, or both, and whether the deductible applies first. Covered California describes it as "an easy-to-read summary that lets you make apples-to-apples comparisons of costs and coverage between health plans." The Texas Department of Insurance states the entitlement: "If you ask, your plan must give you a Summary of Benefits and Coverages."
The full plan document or evidence of coverage. Longer, less readable, and authoritative where the summary is ambiguous.
The member portal. Where the plan shows what it actually applied to a specific claim, and how much of the deductible and out-of-pocket maximum has accumulated so far this plan year.
Plan type also correlates loosely with cost-sharing style, though it does not determine it. The California Department of Insurance notes that plans built on tighter networks are "less likely to have a yearly deductible" and that members "usually pay a co-pay or flat fee for most services," while broader-network plans are more likely to carry a deductible and higher out-of-pocket exposure. Those are tendencies rather than rules, and the letters on a plan are examined in HMO, PPO and EPO.
Where to take a question this article cannot answer. Your plan administrator or benefits contact for what your plan document says. Your insurer's member services for how a specific claim was processed and why. Your state Department of Insurance if a plan will not answer; the National Association of Insurance Commissioners maintains the directory of state departments. A licensed agent for what a specific plan form contains. Anything about the care itself belongs with your clinician, and nothing here interprets a diagnosis or a result.
How the deductible, coinsurance and out-of-pocket maximum fit together as one sequence is set out in how a health plan actually pays.
Frequently asked questions
What is the difference between a copay and coinsurance?
A copay is a fixed dollar amount for a covered service. Coinsurance is a percentage of the allowed amount for that service, which the Texas Department of Insurance defines as "the maximum amount a plan will pay for a covered health care service." The copay is known before the care; the coinsurance amount is not known until the claim is processed.
Do I pay a copay and coinsurance for the same service?
Usually one or the other applies to a given service, but plans can combine cost sharing across an episode of care, so a visit may carry a copay while imaging ordered at that visit carries coinsurance. The Summary of Benefits and Coverage lists which applies by service category.
Does coinsurance start before the deductible is met?
No. The Texas Department of Insurance states that "coinsurance kicks in after you have met your plan's annual deductible." Before that point, covered costs are generally yours in full, apart from any services the plan pays for outside the deductible.
Is coinsurance calculated on the doctor's bill?
No. The Texas Department of Insurance defines coinsurance as "calculated as a percent of the allowed amount for the service," and gives the example of a $100 allowed amount where 20 percent coinsurance is $20 and the plan pays $80. The provider's charge is often higher than the allowed amount, so estimates based on the charge come out too high.
Sources: Texas Department of Insurance, "Do you know the difference between a copay and coinsurance?", April 17, 2025. Texas Department of Insurance, "Health insurance glossary," last updated November 8, 2024. Texas Department of Insurance, "Health care coverage guide" (cb005), last updated March 31, 2026. California Department of Insurance, "Health Insurance Costs" and "Compare PPOs, EPOs, and HMOs," no dates shown on those pages. Covered California glossary, no date shown. All accessed and checked August 11, 2026. Dollar amounts quoted are the publishing department's own illustrations and are not presented as typical or current plan amounts. No premium figure, plan recommendation or company comparison appears in this article.
