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).