Coinsurance is a type of cost-sharing agreement between an insurance company and its policyholder. The policyholder agrees to pay a set percentage of covered health care costs, or share in the insurance company's risk, after the deductible has been satisfied and before the insurance company will pay the remainder of the bill.

In health insurance, co-insurance is an agreement between an insurer and an insured. It states that the insurer will cover part but not all of certain medical expenses. This means that policyholders have to pay the deductible and a percentage of the remaining expenses. For example, under the terms of an 80/20 coinsurance plan, the insurer pays 80 percent of the covered cost of medical services, while the insured pays the remaining 20 percent.

In terms of property insurance, coin-insurance requires the insured to insure their property for a certain percentage of its total cash value, also known as the sum insured. This is usually calculated as a ratio, such as 80/20 or 90/10. For example, if a home is insured for 90 percent of its total value, the owner is liable for 10 percent of the total costs in the event of a claim. The insurer covers the remaining 90 percent.

Co-insurance may appear to be a good deal for the insured, but it requires them to pay a set percentage of costs. It’s important to know that it doesn’t commit the insured to share 100% of the cost - instead, it’s a cap of the amount that can be claimed. Therefore, even when a policyholder pays the co-insurance percentage and the insurer covers the remaining costs, it’s possible that the full amount is not covered. The amount that the policyholder must pay depends on the type of policy, the amount of the deductible, and the level of medical coverage included in the policy.

In the end, coinsurance is an agreement between insurers and policyholders that helps spread the risk and costs of health care and insurance claims. While coinsurance can help keep premiums low, it can be expensive if you end up having to pay more than the agreed upon percent of the cost. As such, it’s important to consider all the factors involved when selecting an insurance plan.