Coinsurance in property insurance: the formula, the penalty and where Texas limits it

The coinsurance formula is insurance carried divided by insurance required, multiplied by the loss, minus the deductible. If you carry less than the policy requires, the insurer pays only that fraction of every covered loss, even a small one. The shortfall is the penalty, and the policyholder absorbs it.

Coinsurance is one of the most misunderstood conditions in property insurance. It is also where a Texas candidate has to be careful, because Texas law treats it differently from the textbook version. In Texas, a clause that makes you a coinsurer for fire losses is void in most cases, with a short list of exceptions. This guide shows the formula, a worked example, and exactly where the Texas limit sits.

What is coinsurance in property insurance?

Coinsurance is a condition in a property policy that ties the amount you must insure to the value of the property. The policy states a required level of coverage, usually a stated share of the property's value. If you insure to that level or above, losses are paid in full up to the limit. If you insure below it, you share the loss with the insurer.

The word causes trouble because it has a second meaning. In health insurance, coinsurance is the share of a bill you pay after your deductible. That is a cost-sharing split between you and the insurer on every claim. Property coinsurance is different. It is a penalty rule for being underinsured, and it only bites when the amount you carried falls short of the amount required.

The reason it exists is fairness in pricing. Premium is charged as a rate applied to the limit you buy. If many owners insure a building for far less than it is worth, they pay far less premium, yet most losses are partial and would still be paid in full. Coinsurance removes that advantage by tying the payout to how well the building was insured.

How does the coinsurance formula work?

There are three pieces: the amount you carried, the amount the clause required, and the loss. The insurer compares the first two and applies that ratio to the third.

Two details trip people up:

• The ratio never goes above one. If you carry more than required, you do not get paid more than the loss. You get the loss, up to your limit.
• The deductible comes off last. The ratio is applied to the loss first, and the deductible is subtracted from that reduced figure.

How is the coinsurance penalty calculated?

Take the formula in words rather than numbers. Say the clause requires a certain amount of insurance, and you carried three-quarters of that required amount. The ratio is three-quarters. A covered loss is therefore paid at three-quarters, and then the deductible is subtracted from that result. The missing quarter of the loss is the penalty. You pay it out of pocket.

The table shows how the ratio changes the payment on the same loss.

Two consequences follow from this arithmetic. First, the penalty applies to partial losses, not only total ones. A policyholder who is underinsured is penalized on a small kitchen fire just as much as on a large one. Second, the penalty is invisible until you claim. The policy was issued and the premium was paid, and nothing warned you that your limit had drifted below the required level as construction costs rose.

Which valuation basis does the clause use?

The "amount required" depends on how the policy values the property. A clause may measure against replacement cost or against actual cash value, and the choice changes the number a lot. Replacement cost ignores depreciation. Actual cash value subtracts it. The same building can have a very different required amount under each basis.

That is why coinsurance and valuation are studied together. If you have not read it yet, the explainer on ACV vs RCV covers how depreciation drives the gap. Read the policy's valuation condition before you calculate anything, because applying the right ratio to the wrong value gives the wrong answer.

Does Texas allow coinsurance clauses?

Texas restricts them. Section 2002.005 of the Texas Insurance Code, which you can read on the Texas Legislature's statute site, starts from a prohibition. An insurer may not issue a property policy covering property in Texas that contains a clause that either:

1. requires the insured to obtain or maintain a larger amount of insurance than expressed in the policy, or
2. provides that the insured is liable as a coinsurer for any part of the loss or damage caused by fire.

The statute then says that such a clause is void. In plain terms, a Texas fire policy cannot penalize you for carrying less than a required percentage of value, and the clause does not hold up if one is written into the form.

The prohibition has exceptions, and the exceptions are where exam questions and real policies live:

• Marketed and manufactured goods. Subsection (c) allows a coinsurance clause on cotton, grain, or other products in the process of marketing, shipping, storing, or manufacturing.
• An optional clause for a premium reduction. Subsection (d) lets an insured accept a policy with a coinsurance clause for a class of property other than those goods, a private dwelling, or a retail stock of merchandise valued under $10,000, if the insured is allowed a reduction in the premium rate. A clause under that subsection is valid and binding, and the commissioner may set the premium rates for it.
• Tornado, windstorm and hail. Subsection (e) lets the commissioner by order authorize or require the use of any form of coinsurance clause on policies that insure against those hazards, on any class of property.

So the useful way to hold it in your head is a default and three doors. The default is that coinsurance is void for fire. The doors are goods in commerce, an optional clause taken for a lower rate, and the commissioner's authority over windstorm and hail.

Where does coinsurance show up outside the statute?

Coinsurance is a standard idea in property insurance generally, and many commercial property forms are built around it. It matters to a new agent in a way the statute does not capture. Even where Texas voids the clause for fire, the habit it teaches is sound: insure property to its real value. Underinsurance causes unpaid losses in any state, with or without a formal penalty.

A related protection sits in some policies as an agreed value option, which suspends the coinsurance condition when the insurer accepts a stated value. Whether a form includes that option is a policy question, so read the form rather than assume.

Coinsurance also interacts with the policy type. A broad, all-risk homeowners form and a named-perils form differ in which causes of loss they cover, a distinction the Texas Department of Insurance explains on its home insurance policy types page. Coinsurance does not change what is covered. It changes how much of a covered loss is paid.

What does this mean for you as a candidate or new agent?

Three practical points.

First, memorize the formula as a ratio: carried over required, times the loss, minus the deductible. Questions rarely ask for more than that.

Second, know the Texas default. When a question asks about a fire policy in Texas, the clause that makes the insured a coinsurer is void, with the exceptions above. Do not carry the general rule into a Texas question without checking the statute.

Third, as an agent you will be the person who sets the limit. The penalty exists because the number on the declarations page was too low. Asking about construction costs and keeping limits current protects your clients far better than explaining a penalty afterward.

To check yourself, try the free practice questions on property insurance, and use the Texas P&C exam content outline guide to see where property conditions sit in the outline. If you want a structured plan, the Texas P&C exam prep course covers these conditions in order.

Frequently asked questions

What is the coinsurance formula in property insurance?

The formula is the amount of insurance carried, divided by the amount required, multiplied by the loss, minus the deductible. If you carried less than the clause requires, the ratio is below one and the insurer pays that fraction of the loss. If you carried the required amount or more, the loss is paid in full up to the limit.

Is coinsurance the same as a copay or health coinsurance?

No. Health coinsurance is a percentage of each bill you pay after your deductible. Property coinsurance is a penalty condition that applies only when you insure the property for less than the policy requires. It is a rule about underinsurance, not a routine cost split on every claim.

Does Texas void coinsurance clauses on fire policies?

Mostly, yes. Section 2002.005 of the Texas Insurance Code bars a clause that makes the insured a coinsurer for fire losses and declares such a clause void. Exceptions cover goods in commerce, an optional clause accepted for a lower premium rate on certain property, and windstorm, tornado and hail policies the commissioner authorizes.

Does the coinsurance penalty apply to small losses?

Yes. The ratio is applied to every covered loss, large or small. An underinsured policyholder is penalized on a partial claim exactly as on a total one. The insurer pays the same fraction of each loss and then subtracts the deductible, so even a modest claim can fall well short.

How can you avoid a coinsurance penalty?

Insure the property to the level the clause requires, using the valuation basis the policy names, and review the limit as construction costs change. Some forms also offer an agreed value option that suspends the condition. Check your actual policy, because the requirement and the options are written into the form.