What Is a Coinsurer?

A coinsurer is a company that shares some of the potential liability for covering a single policyholder. The arrangement is most common when the risk or risks covered could be too costly for a single insurance company to cover.

Generally, a primary insurance company covers most of the cost of a major claim while a coinsurer takes responsibility for the rest.

[In health insurance, coinsurance is the share of the costs for care that is owed by the policyholder above and beyond the annual deductible amount. It is the insured person's co-pay for medical bills. For example, an 80-20 policy requires the policyholder to pay 20% of the medical bill while the insurance company picks up the rest.]

Understanding the Coinsurer

Coinsurers share in any claim or loss in proportion to the amount of risk that they take on.

They are most often used for policies covering large businesses and governments that could suffer a loss that is beyond the resources of any individual insurance company. After the attack on New York City's World Trade Center in 2001, seven insurers ultimately paid more than $4 billion in property damage claims. 

The policyholder receives a separate contract from each coinsurer. To reduce the paperwork burden, the insurance company that undertakes the largest proportion of the claim serves as the leading insurer.

When Coinsurers Are Needed

Some types of policies, like industrial fire insurance, typically involve coinsurance because of the high dollar cost of the risks the policy covers.

State or federal laws dictate that some risks must be jointly insured by several coinsurers in order to adequately diversify the risk of a large claim.

Key Takeaways

  • Coinsurers share the risks of coverage for clients whose potential claims are beyond the resources of a single insurer.
  • Reinsurance companies share the excess costs of an unexpected flurry of claims that strain the resources of a primary insurer.
  • Seven coinsurers handled the claims for the World Trade Center attack in 2001.

Insurance companies share risks in various ways, sometimes passing part of the risk to a reinsurance company. Reinsurance, also known as insurance for insurers or stop-loss insurance, is a transferral of a portion of responsibility to another party. The reinsurer accepts responsibility for claims above a certain level in return for a share of the premium paid by the policyholder.

Coinsurance vs. Reinsurance

Reinsurance typically covers an insurance company against an unexpected accumulation of individual claims that would otherwise endanger its solvency.

A coinsurer is one of two or more insurance companies that agrees to share direct responsibility for the payment of claims from a policyholder. A reinsurer agrees to reimburse an insurance company for losses above an anticipated level.

Both practices allow insurers to underwrite policies for a larger number of clients without imperiling their financial stability. Just as a homeowner needs insurance to rebuild after a fire, an insurance company needs coinsurers and reinsurers to cover the costs of too many devastating fires breaking out at the same time.