Coinsurance, and how to keep the penalty off the table
Coinsurance is the clause most likely to shrink a claim check below what an owner expected — and it does it on partial losses, not just catastrophes. Here's exactly how it works and how to avoid it.
What coinsurance actually is
Coinsurance is the single most misunderstood clause in a commercial property policy — and the one most likely to cut a claim check below what an owner expected. A coinsurance clause requires you to carry a limit equal to at least a set percentage of your property's value, commonly 80%, 90%, or 100%. Carry enough, and covered losses are paid in full up to the limit. Fall short, and a penalty reduces every claim — including small, partial ones — in proportion to how underinsured you were.
It is not a deductible and it is not a coverage limit. It is a condition of the policy that quietly tests, at the moment of loss, whether you insured the building to value. A higher coinsurance percentage usually earns a lower rate, precisely because it requires you to carry more insurance.
The formula, and why it bites
The penalty math is simple and unforgiving:
( Limit Carried ÷ Limit Required ) × Loss − Deductible = Amount Paid
The "limit required" is your property's value multiplied by the coinsurance percentage. If your building is worth $1,000,000 with an 80% clause, the required limit is $800,000. Insure it for less, and the ratio of carried-to-required becomes a multiplier applied to your loss.
A worked example
The invisible $12,500
A building is worth $1,000,000 with an 80% coinsurance clause — required limit $800,000. The owner insured it for only $700,000. A $100,000 loss occurs (well short of total). The ratio of carried to required is 700,000 ÷ 800,000 = 0.875. The insurer pays 0.875 × $100,000 = $87,500. The owner absorbs $12,500 — not because of any deductible, but purely because the building was underinsured.
Coverage is illustrative only and governed solely by the issued policy.
Coinsurance penalizes partial losses just as harshly as total ones. Most owners assume underinsurance only matters in a catastrophe — it matters on every claim, and the penalty is invisible until the loss is filed.
Why owners end up underinsured without deciding to
Underinsurance is rarely a decision — it's drift. Two forces erode your insurance-to-value ratio constantly: rising construction and material costs, and limits set once and never revisited. A limit that was accurate three years ago can be 20% short today after construction inflation, with nothing on the policy signaling the gap. The clause doesn't care why you're short; the math applies either way.
How to take coinsurance off the table
There are two reliable defenses:
- Agreed value. The insurer and insured agree on the property's value up front, which suspends the coinsurance clause for the policy term. It usually requires a signed statement of values, generally resubmitted at renewal to keep the arrangement in force. This is available by endorsement, subject to underwriting.
- Keep values current. Review your limits at least annually and whenever the business or its inventory changes materially. It's the cheapest defense against the inflation-driven penalty.
How your limit is spread: specific, scheduled, blanket
How a limit is arranged across your property changes how it responds at claim time:
- Specific insurance — a dedicated limit for a single building or item.
- Scheduled insurance — each item or location listed with its own limit; precise, but no flexibility to shift limits when a loss hits.
- Blanket insurance — one limit covering several buildings, locations, or property types. Flexible at claim time, but it relies on accurate reported values, and a margin clause (say, 110% of a location's reported value) can cap how much of the blanket limit is available at any single location.
For businesses whose inventory swings seasonally, a value reporting form (periodic value reporting with premium adjusting to match) or a peak season endorsement (automatic higher limits for a defined high-inventory period) keep coverage aligned with value and avoid an underinsurance penalty at the worst moment.
Frequently asked questions
No. A deductible is a fixed amount you absorb on every claim. Coinsurance is a condition testing whether you insured the property to a required percentage of its value; if you didn't, a proportional penalty reduces the payout on top of the deductible.
It depends on the risk and how confident you are in the insured value. Higher percentages (90–100%) usually earn lower rates but demand more accurate valuation. Agreed value removes the guesswork entirely by suspending the clause for the term.
Yes — this is the key point. The penalty applies proportionally to every covered loss, not just total losses, which is why underinsurance can quietly reduce even a modest claim.
Insure to the required value and keep it current, or place the policy on an agreed value basis (available by endorsement, subject to underwriting), which suspends the clause for the term.