A copayment, or copay, is a flat dollar amount paid for a medical service by an insured. Insurance companies use copayments to share health care costs.

In the US insurance market, coinsurance is the joint assumption of risk between the insurer and the insured.

Coinsurance is expressed as a percentage or pair of percentages generally with the insurer's portion stated first. The maximum percentage the insured will be responsible for is generally no more than 50%. Coinsurance indicates how an insurer and an insured will share the costs of a bill that exceeds the insurance policy's deductible up to the policy's stop loss. Once the insured's out-of-pocket expenses equal the stop loss the insurer will assume responsibility for 100% of any additional costs.

In the international insurance market, coinsurance is the joint assumption of risk between various insurers.

Coinsurance is generally widely used in the European insurance market. In this context, a common insurance contract is used and the risk is shared based on percentages between the insurance companies. Often, one insurance company will lead. When leading the insurance company will be responsible for administering various aspects of the insurance policy, such as premium, any claims and the insurance documents. In this situation, a charge is levied (termed Lead Office commission).

In an insurance policy, the deductible or excess is the portion of any claim that is not covered by the insurance provider. It is normally quoted as a fixed amount and is a part of most policies covering losses to the policy holder. The deductible must be "met", that is, paid by the insured, before the benefits of the policy can apply.

In a typical automobile insurance policy, a deductible will apply to claims arising from damage to or loss of the policy holder's own vehicle, whether this damage/loss is caused by accidents for which the holder is responsible, vandalism or theft. Third-party liability coverage generally has no deductible, since the third party will likely attempt to recover any loss, however small, for which the policy holder is liable.

Most health insurance policies and some travel insurance policies have deductibles as well. Typically, a general rule is: the higher the deductible, the lower the premium, and vice versa.

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