Coinsurance
Coinsurance is a property insurance clause requiring you to insure at least a stated percentage of a property's value, often 80% to 100%. If you carry less, claim payments are reduced proportionally. In health insurance, it means your percentage share of a covered cost.
Last updated October 13, 2026
How coinsurance works
In commercial and homeowners property policies, a coinsurance clause sets a minimum amount of insurance relative to the value of the covered property at the time of loss, often 80%, 90% or 100%. IRMI explains the purpose as keeping premiums fair across policyholders: someone who insures only part of a building's value should not pay the same rate as someone who insures all of it.
The usual recovery formula is:
- Insurance required = coinsurance percentage x value of the property at the time of loss (replacement cost or actual cash value, whichever the policy uses)
- Payment = (insurance carried / insurance required) x loss, then less the deductible
If you carry at least the required amount, no penalty applies. If you carry less, you absorb a proportional share of every covered loss, including small ones.
Example
A building is worth $1,000,000 and the policy has an 80% coinsurance clause, so $800,000 of insurance is required. The owner carries $600,000. A covered loss of $100,000 occurs. The payment is $600,000 / $800,000 = 75% of the loss, or $75,000, and the $5,000 deductible reduces it to $70,000. The owner bears the other $30,000 plus the deductible.
Valuation matters
The required amount is based on value at the time of loss, using the valuation basis in the policy. If the policy pays on replacement cost, the requirement is measured against replacement cost, not depreciated value. Checking the valuation clause on the declarations page tells you which basis applies.
What to watch for
- Outdated values. Construction and equipment costs change. A limit that met the requirement at purchase may not at the time of loss.
- Business income. IRMI notes that a sudden rise in income can increase the required amount mid-year on business income coverage.
- Agreed value. An agreed amount endorsement may suspend the coinsurance requirement for the policy period if the insurer accepts your stated value. Availability and conditions vary.
- Same word, different meaning. In health insurance, coinsurance is the percentage of a covered cost you pay after your deductible. That is a cost-sharing feature, not a penalty formula.
Coinsurance vs. related terms
- Coinsurance vs. deductible. A deductible is a dollar amount you absorb on each loss. A coinsurance clause is a condition on how much insurance you carry. Both can apply to the same claim: the coinsurance ratio reduces the loss payment first, and the deductible is then subtracted, as in the formula above.
- Coinsurance vs. limit. The limit is the most the policy will pay. The coinsurance clause tests whether that limit is high enough relative to value, and reduces payment if it is not.
- Coinsurance vs. agreed value. An agreed value endorsement can suspend the clause for the policy period if the insurer accepts your stated values. Without it, the clause is tested at the time of loss.
- Property coinsurance vs. health coinsurance. The word is shared but the meaning is not. In health plans it is a cost-sharing percentage. In property policies it is an insurance-to-value requirement.
- Coinsurance vs. a hammer clause. In some liability policies, a coinsurance hammer clause splits later costs between insurer and insured after the insured declines a recommended settlement. That is a different mechanism from the property clause. See consent to settle.
Second example: values that fell behind
A hypothetical hardware lab buys a property policy with a 100% coinsurance clause when its equipment has a replacement cost of $1,200,000, and sets the limit at that amount. A year later, after purchasing more equipment and with higher replacement prices, the same property would cost $1,500,000 to replace. The requirement is now $1,500,000, and the lab still carries $1,200,000, which is 80% of what is required. A covered loss of $50,000 occurs. The insurer pays 80% of the loss, or $40,000, and then subtracts a $5,000 deductible, so the lab receives $35,000. The lab pays the other $15,000 and the deductible, even though the loss was small and well under the limit.
Questions to ask your broker or underwriter
- What coinsurance percentage applies to each coverage and each location, and does any coverage waive it?
- Is value measured at replacement cost or actual cash value?
- Can we add an agreed value endorsement, and what must we provide to qualify?
- Does the policy use a blanket limit or a margin clause, and how do those interact with the coinsurance requirement?
- How and when were our insured values last updated, and who owns the update process?
- How is the requirement worked out for business interruption, and does it depend on a worksheet we complete?
Why it matters for technology, AI, fintech and digital-asset companies
Hardware, data center and lab-based companies can hold equipment whose replacement cost changes quickly. If values are not refreshed, the limit can fall behind and a coinsurance shortfall can reduce a property claim. See property insurance for general background.
Replacement cost can move quickly for GPUs, networking gear, lab instruments and robotics hardware, and for tenant improvements in leased space. Companies that grow fast also add equipment between renewals, so the schedule of values can go stale within the policy year. Data center operators and hardware makers should refresh values before renewal and after large purchases. See data center insurance and physical AI and hardware for how property programs are typically built, and property insurance and first-party coverage for background.
Related terms
Frequently asked questions
What is coinsurance?
Coinsurance is a property insurance clause requiring you to insure at least a stated percentage of a property's value, often 80% to 100%. If you carry less, claim payments are reduced proportionally. In health insurance, it means your percentage share of a covered cost. The reduction, often called a coinsurance penalty, applies even to partial losses.
What is a coinsurance penalty?
A coinsurance penalty is the reduction in a property claim payment that applies when the amount of insurance carried is below the amount the coinsurance clause requires. The insurer pays only the proportion of the loss that carried insurance bears to required insurance, less the deductible.
How can I avoid a coinsurance penalty?
Insure to at least the required percentage of current replacement value, review values regularly, and ask about an agreed value endorsement that can waive the requirement for the policy period. Your broker or insurer can explain which options your policy and carrier allow.
Is coinsurance the same in health insurance?
No. In health plans, coinsurance is the percentage of a covered service you pay after meeting your deductible, such as 20%. In property insurance, it is a condition on how much insurance you must carry to avoid a reduced claim payment.
How is coinsurance calculated?
First work out the insurance required: the coinsurance percentage multiplied by the value of the property at the time of loss. Then divide the insurance you carry by the insurance required, multiply by the loss, and subtract the deductible. If you carry at least the required amount, no reduction applies.
What does an 80% coinsurance clause mean?
It means you must carry insurance equal to at least 80% of the value of the covered property at the time of loss, using the valuation basis in the policy. If you carry less, claim payments are reduced in proportion. Other common percentages are 90% and 100%.
Does coinsurance apply to liability insurance?
Standard liability policies generally do not have a property-style coinsurance clause. The word does appear in some liability policies in a coinsurance hammer clause, which shares later costs between insurer and insured if the insured refuses a recommended settlement. That works differently.
Does a coinsurance penalty apply to a total loss?
A payment can never exceed the limit carried. If the limit is lower than the value of the property, a total loss leaves the owner with an uninsured shortfall. The ratio formula matters most on partial losses, where the shortfall in coverage reduces each payment.
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