What it means
The two common meanings share one idea: the insurer wants the policyholder to keep some skin in the game. If a business could insure a $2,000,000 building for $500,000 and still recover small losses in full, everyone would underinsure and premiums for genuine cover would become unaffordable.
Property coinsurance clauses set a required level of cover, most often 80%, 90% or 100% of the replacement value. If you carry less than the required amount, the insurer pays only the proportion of your loss that your cover bears to the required cover, and the shortfall lands on you.
This penalty applies to partial losses, which is where most people are caught out, because partial losses are far more common than total ones. A business that insures a building for three quarters of the required amount will find that a kitchen fire costing $400,000 is only ever going to be paid at three quarters, however far below the policy limit that claim sits.
In health insurance, coinsurance works differently and more simply. Once the annual deductible is met, the patient pays an agreed percentage of each subsequent bill, commonly 10% to 30%, until the annual out of pocket maximum is reached, after which the insurer covers everything.
The practical defence in a business context is regular revaluation. Building costs, plant prices and rebuild costs move, so a sum insured that satisfied an 80% clause four years ago can quietly fall below it, and nobody discovers this until a claim is being assessed.
In practice
Real-world examples.
Example
A restaurant group insures its fit out for $600,000 when replacement cost has risen to $900,000, against a 90% clause requiring $810,000. A $150,000 flood claim is settled at roughly 74% of the loss, leaving the group $39,000 short before the deductible is even applied.
Example
An employee with a health plan carrying a $1,500 deductible and 20% coinsurance receives an $8,000 hospital bill. She pays the $1,500 deductible plus 20% of the remaining $6,500, which is $1,300, so her total contribution is $2,800 and the insurer pays $5,200.
Example
A manufacturer revalues its plant annually after a broker warns that machinery replacement costs have risen 18% in two years. The sum insured is increased at a premium cost of $6,400 a year, which removes a coinsurance exposure the broker estimated at several hundred thousand dollars.
Think of it
“Coinsurance is your percentage share-you pay a portion after the deductible.
Formula
Calculation
Claim payment = (insurance carried / insurance required) x loss, less any deductible
A distribution business owns a warehouse with a replacement value of $2,000,000. Its policy carries an 80% coinsurance clause, so the required cover is $2,000,000 x 0.80 = $1,600,000. The business has insured the building for $1,200,000 and carries a $10,000 deductible.
A fire causes $400,000 of damage. The coinsurance ratio is $1,200,000 / $1,600,000 = 0.75, so the insurer's share is 0.75 x $400,000 = $300,000. After the $10,000 deductible, the payout is $290,000.
The business absorbs $400,000 - $290,000 = $110,000 of a loss it believed was fully insured, simply because its sum insured was $400,000 short of the required level.Case study
Seen in the real world.
The following is an illustrative and entirely fictional example. Alder Bay Cold Storage, an invented refrigerated warehousing business, insured its main facility for $3,000,000 when it was built and never revisited the figure. Eight years later, construction and refrigeration plant costs had risen enough that full replacement value stood at $4,600,000, and the policy carried a standard 80% coinsurance clause.
A compressor failure caused a fire that destroyed one chamber, with an assessed loss of $920,000. The required cover was $3,680,000, the company carried $3,000,000, and the resulting ratio of about 81.5% meant the insurer settled at roughly $750,000 before the deductible. Alder Bay's fictional finance director had to fund the remaining shortfall from the company's overdraft facility.
The lesson drawn in this illustrative story was not that the insurer behaved badly but that nobody owned the sum insured. Alder Bay added an annual revaluation to the finance calendar, at a cost of a few thousand dollars a year in broker and valuation fees.
Watch out
Common mistakes.
- Believing the coinsurance penalty only bites on total losses, when it applies to every partial claim and partial claims are far more common.
- Insuring a property for its market value rather than its replacement cost, which are very different numbers and often move in opposite directions.
- Confusing coinsurance with the deductible, when the deductible is a fixed first slice of every claim and coinsurance is a proportional share.
Questions
People also ask.
How do I avoid a coinsurance penalty?
Insure the asset for at least the percentage of replacement value the clause requires and revalue it at least annually.
Is a higher coinsurance requirement worse for me?
Not necessarily, since a higher required percentage usually comes with a lower premium rate, but it does demand far more accurate valuation.
Does coinsurance apply to business interruption cover?
Yes, many business interruption policies contain a similar clause based on annual gross profit, and understating that figure produces exactly the same proportional reduction.
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