Coinsurance

What Is Coinsurance?

Coinsurance is a cost-sharing rule that divides the cost of a covered loss between the policyholder and the insurance company by percentage. Instead of paying a fixed dollar amount, the policyholder pays a set share and the insurer pays the rest. The split is often written as two numbers, such as 80/20, where the first number is the insurer's share and the second is the policyholder's share.

Coinsurance appears most often in health insurance and commercial property insurance, though the mechanics differ between the two. In both cases, it is one of several tools insurers use to share risk and discourage unnecessary claims.

How Coinsurance Works in Health Insurance

In a health plan, coinsurance usually applies after the deductible has been met. Suppose a plan has an 80/20 coinsurance arrangement and a provider bills $1,000 for covered care after the deductible is satisfied. The insurer would pay $800 and the patient would pay $200.

Coinsurance is typically limited by an out-of-pocket maximum. Once the policyholder's share of covered costs reaches that cap during the plan period, the insurer pays the full amount of additional covered costs. Without this limit, a serious or long illness could create very large personal costs.

Coinsurance differs from a copayment, which is a fixed dollar amount per service. A copayment stays the same regardless of the bill, while coinsurance rises and falls with the total cost.

Coinsurance in Property Insurance

Some property policies include a coinsurance clause requiring the owner to insure a building for a minimum percentage of its full replacement value, such as 80 percent. If the coverage carried is below that required share, the insurer may reduce a claim payment proportionally. This penalty is a consequence of underinsurance, and it often surprises property owners who have not updated their coverage as construction costs or property values changed.

Why It Matters to Policyholders

Coinsurance affects how much of a bill a person ultimately pays and how predictable those costs are. Because the policyholder's share grows with the bill, a higher percentage can lead to large costs for expensive care or repairs. Reviewing the coinsurance rate, the deductible, and the out-of-pocket maximum together gives a clearer picture of potential exposure than any one term alone. Policy wording varies, so the exact terms in a specific contract are the ones that govern.