The coinsurance requirement is a commercial property policy condition that obligates the insured to maintain insurance equal to at least a specified percentage — typically 80%, 90%, or 100% — of the property's full replacement cost value at the time of a loss. If the insured carries less than the required percentage, any partial loss recovery is reduced proportionally by a coinsurance penalty. The clause exists to prevent insureds from intentionally underinsuring property on the theory that they are unlikely to sustain a total loss.
How It Works / Why It Matters
The coinsurance formula is standard: Recovery = (Amount carried / Amount required) × Loss, subject to the policy limit.
Example: A commercial building has a replacement cost of $2,000,000. The policy has an 80% coinsurance requirement, meaning the insured must carry at least $1,600,000 of coverage. The insured actually carries $1,200,000.
If the building suffers a $400,000 partial loss:
Recovery = ($1,200,000 / $1,600,000) × $400,000 = 0.75 × $400,000 = $300,000
The insured recovers only $300,000 of a $400,000 loss — the $100,000 shortfall is the coinsurance penalty the insured bears for underinsuring by 25%. The insured is penalized even though the carried limit ($1.2M) is three times the loss amount ($400,000).
The economic logic from the carrier's perspective: the carrier charges a rate per $1,000 of insured value. If all insureds carried only 50% of replacement cost, the carrier would collect half the premium it needs to pay expected losses (since losses are roughly proportional to value at risk). The coinsurance clause ensures that insureds who underinsure bear a portion of their own losses, creating an incentive to insure to value.
Higher coinsurance percentages (90% or 100%) may qualify for a lower rate, because the carrier is confident the premium is adequate to cover expected losses. An 80% coinsurance clause costs more per $1,000 than a 100% clause because the carrier accepts more underinsurance risk.
In Practice
Coinsurance is one of the most misunderstood commercial property concepts for both agents and insureds. Many insureds believe that buying any amount of insurance less than a total loss value is acceptable, not realizing that underinsurance below the coinsurance threshold reduces recovery even on small partial losses.
The most common cause of coinsurance problems is outdated property values. A building insured at $1 million in 2018 may have a replacement cost of $1.6 million in 2024 due to construction cost inflation — and if the policy has not been updated, the insured is now underinsured relative to any 80% or 90% coinsurance requirement. Agents should conduct annual replacement cost reviews with commercial property clients and recommend coverage updates when values have appreciated significantly.
Valuation tools from Verisk — specifically the 360Value replacement cost estimator — are widely used to calculate accurate replacement costs for commercial and residential properties, providing a defensible basis for the insured value on coinsurance-bearing policies.
Agreed value coverage is the mechanism carriers use to suspend the coinsurance clause: when the carrier and insured agree at inception that the stated value represents the full insurable value, the coinsurance penalty does not apply. Agreed value policies require careful value documentation at inception and periodic reappraisal.
Blanket vs. specific coverage interacts with coinsurance at the portfolio level. On a blanket policy, the coinsurance test uses the total insurable value of all covered property — a partial loss anywhere triggers a coinsurance calculation based on whether the blanket limit is adequate relative to the total portfolio value.
Related Concepts
The statement of values (SOV) — a schedule documenting each covered location's replacement cost — is the practical tool for verifying coinsurance compliance on multi-location commercial accounts. Agents should maintain current SOVs and update them annually or when significant property changes occur.