Home insurance coinsurance: what being underinsured actually costs
A homeowners or commercial property policy can shortchange you two different ways, and they're easy to confuse: your Coverage A limit might simply be lower than what it would actually cost to rebuild, and separately, a coinsurance clause can shrink even a partial-loss payout if you're insured below a required percentage. Checking both takes three numbers and two small calculations.
The method
Coverage gap = replacement cost value (RCV) − your Coverage A limit — how much of a full rebuild your limit wouldn't cover. Percent insured = limit ÷ RCV × 100 — compare that to the coinsurance percentage your policy requires (commonly 80%). Meet or beat it, and a partial loss pays out in full up to your limit; fall short, and the insurer can pay out less than the damage, proportionally.
A policy that meets its requirement
A home has a $400,000 replacement cost, insured for a $320,000 Coverage A limit, with an 80% coinsurance requirement.
- Percent insured:
320,000 ÷ 400,000 × 100 = 80%— exactly meets the requirement. - Coverage gap:
400,000 − 320,000 = $80,000.
That $80,000 gap doesn't trigger a coinsurance penalty — the policy meets its 80% requirement, so a partial loss pays out in full up to the limit. But the gap still matters in a total loss: the policy pays at most $320,000, so rebuilding a $400,000 home still leaves $80,000 to cover another way.
The real cost of falling short
Now a different property: $250,000 replacement cost, insured for only $180,000, same 80% requirement.
- Percent insured:
180,000 ÷ 250,000 × 100 = 72%— short of the 80% requirement. - Coverage gap:
250,000 − 180,000 = $70,000.
Falling short of the coinsurance requirement doesn't just mean a bigger gap in a total loss — it also docks a partial loss. The standard coinsurance penalty works like this: required insurance = coinsurance % × RCV, or 0.80 × 250,000 = $200,000 here. The insurer pays a claim in the same proportion as what you carried to what you should have carried: 180,000 ÷ 200,000 = 0.9, or 90 cents on the dollar. A $50,000 kitchen fire, in that case, pays out 50,000 × 0.9 = $45,000 — a $5,000 penalty on top of any ordinary deductible, purely for being underinsured relative to the requirement, even though the fire damage itself was well under the policy limit.
Why these are two different problems
The dollar gap (RCV minus limit) is about a total loss: it's the difference between what a full rebuild costs and what the policy would ever pay, no matter how well-insured you are relative to the coinsurance rule. The coinsurance percentage is about a partial loss: it can cut a payout even on damage far smaller than your limit, purely because your limit sits below the required share of replacement cost. A property could clear the coinsurance test and still carry a large total-loss gap, or fail the coinsurance test on a policy whose limit is close to adequate — they're independent checks, and a policy worth trusting needs to pass both.
Two things this doesn't tell you
Replacement cost value isn't the same as market value or purchase price — it's what rebuilding would actually cost today, and it changes with construction costs, so an RCV set years ago can drift low without anyone updating the policy. Second, the exact coinsurance clause language, the required percentage, and how strictly it's enforced all vary by insurer and policy — confirm both numbers on your own declarations page rather than assuming 80% or any other figure applies.
Run your own numbers
The free Insurance Policy-Limit Gap tool checks your own replacement cost, limit and coinsurance requirement instantly, entirely on your device.