Commercial Property Coinsurance Calculator Guide
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Commercial property coinsurance can reduce a partial-loss payment when the limit carried is below a stated percentage of the covered property value. It is an insurance-to-value condition, not the percentage cost sharing used in health insurance.
Calculate required limit and coverage ratio
required limit = property value at loss × coinsurance percentage. Then coverage ratio = min(1, limit carried ÷ required limit). The calculator applies that ratio to eligible loss, subtracts the entered deductible, floors payment at zero and caps it at the property limit.
Worked 80% example
If replacement value is 1,000,000 and the condition is 80%, the required limit is 800,000. Carrying 600,000 produces a 75% ratio. On a 250,000 eligible loss with a 10,000 deductible, the illustration is 177,500 before any different policy wording: 250,000 × 75% − 10,000.
Use the policy-defined value—not a convenient number
Market price, tax value, book value, original purchase price and reconstruction cost are not interchangeable. Include covered building features, equipment, inventory and other property under the correct schedule. Exclude land when the form does not insure it.
Verify agreed value or another waiver
California insurance guidance describes agreed value as a method that can waive a coinsurance penalty. The signed statement, valuation evidence, endorsement, effective dates and renewal requirements matter. A waiver does not create unlimited coverage.
Keep penalty, deductible and limit separate
The deductible is retained even when the coinsurance requirement is met. The policy limit can cap a large loss even when no penalty applies. The “loss not paid” total can therefore include deductible, penalty, limit shortfall and exclusions.
Check provisions outside the simple formula
Blanket limits, margin clauses, reporting forms, inflation guard, peak-season endorsements, debris removal, ordinance or law, vacancy, protective safeguards, valuation conditions and replacement-cost timing can change settlement. The tool does not interpret them.
Run both written programs against the same property loss
The Business Insurance Coverage Gap & Cost Comparison Calculator shows required limit, ratio, payment without penalty, modeled payment, coinsurance penalty, limit shortfall and retained property cost for Program A and Program B.
Frequently asked questions
Does carrying 80% of value mean the insurer pays 80% of every loss?
No. The 80% condition sets a required limit. When the carried limit meets it, the ratio in this simplified formula is 100%, subject to deductible, limit and policy terms.
Does replacement cost guarantee a full replacement payment?
No. Eligibility, valuation conditions, timing, limits, deductibles, exclusions and proof requirements still apply.
Does CalculatorGeek sell business insurance or collect quote leads?
No. The calculator and guides do not rank carriers, display live offers, collect applications, sell leads, predict eligibility, or recommend a policy.
Do the USD, GBP, CAD and AUD modes apply local insurance law?
No. They change currency formatting and context only. They do not insert compulsory cover, taxes, policy forms, premiums or legal duties.
Sources and review status
- California Department of Insurance — Commercial Insurance Guide
- NAIC — Small Business Insurance
- U.S. Small Business Administration — Get Business Insurance
- UK Business.gov — Insuring Your Business
- Business.gov.au — Types of Business Insurance
- BDC — What Business Insurance Do You Need?
Sources and model boundaries were checked on 2026-10-08. CalculatorGeek Editorial Team reviewed and approved the full finance and insurance package on 2026-10-08. The cited organizations supplied source material; they did not review or endorse this CalculatorGeek package. Product terms, policy forms, laws, regulatory guidance and rates can change; current written documents and applicable authorities control.
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