What a Coinsurance Clause Actually Means

Homeowners assume the coverage limit on their declarations page is the most they can lose. In many policies it is not. A coinsurance clause lets the insurer pay less than the stated amount if your coverage limit is low relative to the value of the property, and it is the single most misunderstood provision in the policy.

The 80 percent rule

The typical clause states that you must carry dwelling coverage of at least 80 percent of the property's replacement value. If your limit is below that threshold, your claim is reduced in proportion to the shortfall. The arithmetic is unforgiving because the penalty is proportional rather than a flat deduction.

How the reduction is calculated

The formula is straightforward once you have the two inputs:

Amount insured pays = (Coverage limit ÷ Required limit) × Loss

Where the required limit is 80 percent of replacement value. Work an example. Suppose replacement value is 400,000 dollars, so the required limit is 320,000 dollars, but the policy carries only 200,000 dollars of coverage. The insurer pays 200,000 divided by 320,000, which is 62.5 percent of the loss. On a 100,000 dollar claim you receive 62,500 dollars and must fund the remaining 37,500 dollars yourself, even though you were not underinsured by accident in any meaningful sense.

How replacement value is established

Insurers do not accept your estimate uncritically. They use a replacement cost estimator that pulls local construction costs, square footage, year built and finish quality. Two owners with identical buildings can receive different replacement values depending on local input costs, which means your personal estimate may differ from the insurer's by a wide margin. Request a formal replacement cost estimate in writing so you know the number the insurer is using.

The renovation problem

Homeowners routinely under-insure because they base the limit on what they paid years ago or on the mortgage balance. Adding a kitchen, bathroom or finished basement raises replacement value substantially and should raise the limit to match. A kitchen renovation of 40,000 dollars can push a 400,000 dollar estimate to 450,000 dollars, which moves the required coverage threshold with it. Review the limit after every significant renovation.

How to eliminate the clause

1. Obtain the insurer's written replacement cost figure for your property.
2. Add twenty percent to it, since building costs generally rise.
3. Set your dwelling coverage limit to that number rather than the mortgage balance.
4. Ask specifically whether a coinsurance clause exists and what percentage it uses.
5. Check whether an extended replacement cost endorsement raises the settlement ceiling further.

Use our home insurance calculator to work out the limit that keeps you compliant, and then compare that figure to the limit currently printed on your declarations page.