Coinsurance and insurance-to-value calculator
Test your dwelling limit against the 80% insurance-to-value rule and see how much a partial loss claim shrinks if you fall short.
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Most homeowners policies pay full replacement cost on a partial loss only if your dwelling limit is at least 80% of the cost to rebuild the whole house. Fall below that line and every claim shrinks, even a small one. The calculator shows by how much.
How to use it
Enter six numbers:
- Cost to rebuild the whole house today. Use a current estimate; the home replacement cost estimator or your insurer's valuation will do. Market value is the wrong number.
- Your dwelling limit (Coverage A), from the declarations page.
- The repair cost of the damage you are testing, at replacement cost.
- Depreciation on the damaged part, as a percentage. The adjuster sets this; the default of 30% is only an example.
- Your deductible.
- The insurance-to-value requirement. The standard form uses 80%; read the loss settlement condition in your policy.
How the math works
The required limit is the requirement times the rebuild cost. If your limit meets it, the claim pays the repair cost minus the deductible, capped at your limit. If not, the tool computes two figures and pays the larger, the way the standard form does: the actual cash value of the damage (repair cost times one minus depreciation, minus the deductible), and a proportional payment (your limit divided by the required limit, times the repair cost). It pays the larger of the two, then takes off the deductible, and never pays more than your limit.
Say, hypothetically, a $400,000 rebuild cost and a $280,000 limit. The 80% requirement is $320,000, and you hold 70% of rebuild cost, so the ratio is 0.875. On a $50,000 repair with a $1,000 deductible and 30% depreciation, a compliant policy would pay $49,000. Here actual cash value is $35,000 ($34,000 after the deductible) and the proportional figure is 0.875 × $50,000 = $43,750 ($42,750 after the deductible), so the claim pays $42,750 and you absorb $7,250. Raising the limit to at least $320,000 restores full replacement cost on partial losses; $400,000 also covers a total loss.
What it assumes
The 80% rule and the two-way comparison follow the loss settlement condition of the standard ISO homeowners 3 form (HO 00 03 05 11, May 2011 edition, published by the Maine Bureau of Insurance). Under it, a building insured for less than 80% of full replacement cost is paid the greater of actual cash value or the proportion that the insurance bears to 80% of replacement cost. Every dollar figure in the tool is an editable example. Depreciation and the repair cost are the adjuster's call, not the calculator's.
Where it stops being right
Your policy, not the standard form, controls. Some insurers write their own wording, require a different percentage, or promise to rebuild if you insure to their estimate; see extended and guaranteed replacement cost coverage. The tool follows the standard form's order: the loss settlement clause fixes the amount payable, and the separate deductible clause takes the deductible out of that amount. An insurer's own form or adjusting practice may apply them differently. The form also holds back payment above actual cash value until repairs are finished, with a short exception for small losses and a 180-day window to say you intend to repair or replace. The tool shows the final settlement, not the timing. See recoverable depreciation: getting the rest of your claim.
Finally, 80% is a floor, not a target. A total loss pays only up to the limit, so a house insured at 80% is short by a fifth of the rebuild cost. underinsured after a disaster: your options describes what that looks like in practice, and inflation guard and automatic coverage increases covers keeping the limit current.
Last reviewed October 10, 2026