7 min read · Last updated October 12, 2026
- The 80% coinsurance rule requires you to insure your home for at least 80% of its full rebuild cost. Fall short, and a partial-loss claim gets paid on a reduced formula, not on your actual repair bill.
- The formula: (amount of dwelling coverage you carry ÷ the required amount, 80% of rebuild cost) × the amount of the loss, with the deductible subtracted last.
- On a $500,000 rebuild-cost home carrying $300,000 in dwelling coverage instead of the required $400,000, a $60,000 partial loss pays $45,000 before the deductible and $44,000 after a $1,000 deductible, not the $59,000 a fully insured homeowner would get.
- U.S. residential rebuild costs rose 3.8% in the twelve months ending July 2026, per Verisk’s own reconstruction-cost index, which is exactly how a dwelling limit that cleared 80% two years ago quietly drops under it today.
If your dwelling coverage sits below 80% of your home’s full rebuild cost, most homeowners policies do not pay your actual repair bill on a partial loss. They run it through a coinsurance formula first. Carry $300,000 against a $500,000 rebuild cost (the 80% minimum is $400,000) and a $60,000 kitchen fire pays $44,000 after the deductible, not $59,000.
We will call the homeowner in that example Teresa, a hypothetical used here only to make the math concrete; she returns in the worked example below. She bought her dwelling limit when she bought the house, never revisited it, and assumed any covered loss would simply be repaired. That assumption is what the 80% coinsurance rule punishes.
In this article
- What the 80% Coinsurance Rule Actually Costs You
- How the Penalty Formula Works
- Why Your Dwelling Limit May Already Be Under 80%
- How to Fix It
- Frequently asked questions
What the 80% Coinsurance Rule Actually Costs You
Most homeowners policies require you to insure your dwelling for at least 80% of what it would cost to fully rebuild it today, not its market value and not what the county tax assessor says it’s worth. Georgia’s Office of Commissioner of Insurance spells this out in its own consumer insurance guide: “Most policies require the policyholder to insure the home to at least 80 percent of the cost to rebuild or replace the home. If you insure the home for less than 80 percent, you will become a coinsurer.”
Becoming a coinsurer means you and the insurer split the loss on every partial claim, in a ratio set by how far under 80% you are, for as long as your dwelling limit stays under the threshold.
A total loss works differently: there is no repair bill to run the formula on, so the policy pays up to your stated limit. But Georgia’s guide flags a separate trap: hitting the 80% minimum does not mean you are insured for full rebuild cost.
Its own example shows a $50,000 rebuild needing only $40,000 in coverage to clear the test, still $10,000 short on a total loss. The 80% coinsurance rule protects you from a partial-loss penalty, not a total-loss shortfall.
How the Penalty Formula Works
The formula itself, confirmed against Georgia’s consumer insurance guide, is:
(Amount of Insurance Carried ÷ Amount of Insurance Required) × Amount of Loss
“Amount required” is 80% of your home’s full rebuild cost. The result is the amount the policy pays before your deductible comes out.
Take Teresa’s case. Her home’s rebuild cost is $500,000. The 80% minimum is $400,000.
She carries $300,000, a gap her premium notice never flagged. A kitchen fire causes $60,000 in damage.
| Dwelling coverage carried | Amount carried | Ratio vs. the $400,000 required | Payout on the $60,000 loss, before deductible | Payout after a $1,000 deductible |
|---|---|---|---|---|
| 60% of rebuild cost (Teresa’s actual coverage) | $300,000 | 0.75 | $45,000 | $44,000 |
| 70% of rebuild cost | $350,000 | 0.875 | $52,500 | $51,500 |
| 80% of rebuild cost (the required minimum) | $400,000 | 1.00, no penalty | $60,000 | $59,000 |
| 100% of rebuild cost | $500,000 | 1.00, no penalty | $60,000 | $59,000 |
Run Teresa’s numbers: $300,000 divided by the $400,000 required is a ratio of 0.75. Multiply by the $60,000 loss and the formula pays $45,000, 75% of the repair cost. Subtract her $1,000 deductible and her check is $44,000.
She covers the remaining $16,000 herself, $15,000 from the penalty and $1,000 from the deductible, on a claim that would have paid $59,000 if her limit had matched the $400,000 required.
Past 80%, the ratio caps at 1.00 and stops improving. Carrying 100% protects a total loss, where the policy limit pays out, but it buys nothing extra against this formula once you have cleared 80%.
Why Your Dwelling Limit May Already Be Under 80%
Nobody’s dwelling limit drops on purpose. It drops because rebuild costs keep rising and the limit does not move unless someone updates it. Verisk, the company that supplies most insurers’ own replacement-cost estimates, reported that total U.S. residential reconstruction costs rose 3.8% in the twelve months ending July 2026, driven mainly by labor rates climbing faster than materials.
A limit that cleared 80% two or three years ago can sit below it today without any change to your policy. Nobody sends a notice when that threshold gets crossed. Your declarations page prints the same dwelling number it printed last year, and the gap becomes visible only when an adjuster runs the formula above.
This is the same mechanic covered in why your dwelling limit may already be too low for a real rebuild: a static dwelling number against a rising rebuild cost is a slow leak. The 80% coinsurance rule is the moment that leak gets priced into an actual claim check.
How to Fix It
There is no federal rule here. This lives in individual policy forms, commonly a “loss settlement” or coinsurance condition each insurer files with your state, regulated state by state, not nationally. North Carolina, for example, requires that any such clause be printed or stamped with the words “coinsurance contract” on the policy itself, under N.C. Gen. Stat. 58-3-15, so a homeowner cannot be surprised by a clause they never saw named.
The fix Georgia’s guide recommends is direct: find out what it costs to fully rebuild your home today, contractor pricing included, and insure for that full amount, not the bare 80% minimum. Ask your agent for a current replacement-cost estimate, not a market-value guess, and raise your limit to match it. This breakdown of dwelling limits falling below replacement cost covers the same gap from the shopping side.
Some insurers also sell a feature Georgia’s guide calls Guaranteed Replacement: it pays the full cost to rebuild your home even if that cost exceeds your policy limit once a total loss is priced out. It is not universal, so ask your insurer by name whether it is available, rather than assuming it is included.
Frequently asked questions
Does the 80% coinsurance rule apply if I file a small claim, not a total loss? Yes. The rule applies specifically to partial losses, repairable damage like a roof, a kitchen fire, or a burst pipe. A total loss is paid up to your stated dwelling limit instead, with no formula applied, which is a different problem: your limit itself may be too low.
What counts as “rebuild cost” for the 80% calculation? It means the full cost to rebuild your home with similar materials today, including labor, materials, profit, and overhead, not its market value, sale price, or county tax assessment. Ask your insurer for a current replacement-cost estimate rather than guessing.
Can I just insure for exactly 80% and be safe? You avoid the partial-loss penalty, but you are not necessarily protected on a total loss, since 80% of rebuild cost is still less than full rebuild cost. Insuring to 100% of current rebuild cost covers both situations instead of only one.
How do I find out if my dwelling limit is already under 80%? Ask your agent for a current replacement-cost estimate on your home and compare it to your declarations page dwelling limit. If your limit is below 80% of that estimate, you are underinsured under the coinsurance formula right now, even if you have never filed a claim.
Does raising my dwelling limit to fix this always raise my premium a lot? It raises your premium somewhat, since you are buying more coverage, but the increase is typically far smaller than the gap this formula creates on an actual claim. Ask your agent for the exact premium difference between your current limit and 100% of rebuild cost before deciding.