Casualty Loss: Definition, Calculation, and Tax Deduction Rules

A casualty loss is a financial loss caused by the sudden, unexpected, or unusual damage, destruction, or theft of property. Under Section 165 of the Internal Revenue Code, these losses can be deductible, but the rules are narrower than most people expect. For personal property, the deduction is generally available only when the loss occurs in a federally or state-declared disaster area, and even then, two statutory reductions shrink the deductible amount before it reaches your return.¹

What Events Qualify

The IRS looks for three characteristics in a qualifying casualty: the event must be sudden, unexpected, and unusual. Sudden means swift rather than gradual. Unexpected means the taxpayer didn’t anticipate or intend it. Unusual means it isn’t a day-to-day occurrence. Events that fit include fires, storms, hurricanes, floods, earthquakes, volcanic eruptions, tornadoes, and vandalism. Theft also qualifies, though the deduction is tied to the year you discover the theft rather than the year it happened, and you can’t claim it while there’s still a reasonable prospect of recovery through a pending claim.¹

The damage must be directly traceable to the specific event. A tree falling on your roof during a windstorm qualifies. Dropping your laptop on the sidewalk does not, because clumsiness isn’t a casualty within the tax code’s meaning.

Gradual damage never qualifies. Rust, corrosion, termite infestations, dry rot, and slow erosion all fail the suddenness test. The line can be thin. A pipe that bursts during an unexpected freeze is a casualty; a pipe that leaks slowly due to aging is not.²

The Declared-Disaster Requirement for Personal Property

For personal-use property, you can deduct a casualty loss only if it results from a federally declared disaster or a state-declared disaster. This restriction, originally enacted for tax years 2018 through 2025 under the Tax Cuts and Jobs Act, was made permanent by P.L. 119-21 starting with tax year 2026. A loss from an isolated house fire, a car theft, or vandalism outside a declared disaster zone produces no deduction, no matter how large.³

A federally declared disaster requires a formal presidential declaration under the Stafford Act. You can verify whether your area qualifies by checking the FEMA website or IRS announcements that identify covered locations and dates.¹

Beginning with tax year 2026, personal casualty losses from state-declared disasters also qualify. A state-declared disaster covers natural catastrophes like hurricanes, earthquakes, tornadoes, and mudslides, plus fires, floods, and explosions regardless of cause. To qualify, the governor of the affected state (or the mayor of the District of Columbia) and the Secretary of the Treasury must jointly determine that the damage is severe enough to warrant applying the casualty loss rules.³

How to Calculate the Loss

Your starting figure is the smaller of two numbers: your adjusted basis in the property or the decrease in fair market value caused by the casualty.¹

Adjusted basis is typically what you paid for the property plus improvements, minus any depreciation you’ve taken. The decrease in fair market value is the difference between what the property was worth immediately before the casualty and what it was worth immediately afterward. Most taxpayers need a professional appraisal to establish these values, though for smaller losses the IRS sometimes accepts other evidence.

Cleanup and repair costs can substitute for a formal appraisal, but only if all five of these conditions are met: the repairs were actually completed; they were necessary to restore the property to its pre-casualty condition; the cost wasn’t excessive; the repairs addressed only the casualty damage; and the property isn’t worth more after repairs than it was before. Repairs that improve the property beyond its original condition won’t be accepted as a measure of the loss.²

Whatever starting figure you calculate must then be reduced by any reimbursement you receive or reasonably expect to receive from insurance, government aid, or legal settlements. This is where people run into trouble. If your property is covered by insurance and you don’t file a claim, you still can’t deduct the portion the insurance would have covered. The IRS treats the insured amount as if you received it. The only piece you can deduct without filing a claim is what the policy wouldn’t have covered anyway, such as your deductible.²

The $100 Floor and 10% AGI Threshold

After subtracting reimbursements, the remaining loss runs through two statutory reductions applied one after the other. Both apply only to personal-use property.

First, each separate casualty event is reduced by $100. If a single storm damages both your home and your car, that’s one event and one $100 reduction. If a storm damages your home in March and a fire damages your garage in October, those are two separate events, and you subtract $100 from each.¹

Second, the combined total of all remaining losses for the year is deductible only to the extent it exceeds 10% of your adjusted gross income. If your AGI is $80,000, you subtract $8,000 from the total. A taxpayer with $12,000 in losses after the $100 floors and an AGI of $80,000 has a deductible loss of $4,000. Smaller losses often produce no deduction at all.⁴

Qualified Disaster Losses Get Better Treatment

Not all disaster losses are treated equally. Losses that meet the IRS definition of a “qualified disaster loss” receive substantially more favorable treatment than standard disaster-area casualty losses.

For qualified disaster losses, the per-event floor increases from $100 to $500, but the 10% AGI threshold is eliminated entirely. You also don’t need to itemize, so taxpayers who take the standard deduction can still benefit. For a large loss, skipping the 10% AGI hurdle often produces a deduction thousands of dollars larger than the standard rules would allow.¹

A qualified disaster loss must be attributable to a major disaster declared by the President under the Stafford Act. The IRS periodically updates Publication 547 and the Form 4684 instructions to identify exactly which declared disasters qualify. Check the current year’s instructions for Form 4684 to see whether your specific disaster falls into this category.⁵

Business and Income-Producing Property

Casualty losses on business assets and income-producing property like rental real estate play by friendlier rules. The declared-disaster requirement doesn’t apply, so a fire at your warehouse or flood damage to a rental property is deductible regardless of whether a disaster was declared.

The calculation differs too. If business or income-producing property is completely destroyed, your loss is simply the adjusted basis minus any salvage value and insurance reimbursement. The “lesser of basis or FMV decline” limit that applies to personal property doesn’t apply to completely destroyed business property.¹

The $100 per-event floor and the 10% AGI threshold don’t apply either. Business casualty losses are reported on Section B of Form 4684, and the deductible amount flows to the appropriate business form rather than to Schedule A.⁶

When Insurance Pays More Than Your Basis

Sometimes insurance pays out more than your adjusted basis in the destroyed property. When that happens, you have a taxable gain rather than a deductible loss. It’s more common than you’d expect with homes or vehicles that have appreciated significantly or been heavily depreciated.

You can defer that gain by purchasing replacement property similar in use. The replacement must be bought within two years after the close of the first tax year in which any part of the gain is realized. For property destroyed in a federally declared disaster, the replacement period stretches to four years.⁷

If the replacement costs at least as much as the insurance proceeds, the entire gain is deferred. If it costs less, you recognize gain to the extent the insurance money exceeds what you spent. You elect the deferral on your return for the year you receive the insurance proceeds.

How to Claim the Deduction

Every casualty loss deduction starts with Form 4684, Casualties and Thefts. Section A handles personal-use property; Section B covers business and income-producing property. You need a separate Form 4684 for each casualty or theft event.⁸

For personal losses under the standard rules, the deductible amount flows from Form 4684 to Schedule A. You must itemize to claim the deduction. If your total itemized deductions don’t exceed the standard deduction, the casualty loss provides no tax benefit under the standard path. Qualified disaster losses can be deducted even when you take the standard deduction.⁵

Electing to Deduct in the Prior Year

If your loss occurred in a federally declared disaster area, you can elect to deduct it on the prior year’s return instead of waiting to file the current year’s. That puts cash back in your hands faster through an amended return and refund. The election must be made within six months after the due date of your disaster-year return, not counting extensions. Once made, it can be revoked only within 90 days of the election deadline.⁹

One trade-off: the prior year’s AGI is used to calculate the 10% threshold. If you earned more in the prior year than the disaster year, the deduction could end up smaller. Run the numbers both ways before making the election.

Documentation You’ll Need

The IRS audits casualty loss deductions, and the burden of proof falls on you. Assemble your documentation before you file. The records generally fall into four categories:

Proof of the event: police reports, fire department reports, weather service records, FEMA disaster codes, or IRS disaster announcements establishing what happened, when, and where.
Proof of ownership and value: purchase receipts, deeds, titles, contracts, and pre-casualty photographs. For the fair market value decline, professional appraisals or detailed repair estimates showing values before and after.
Insurance records: filed claims, correspondence with your insurer, and documentation of all reimbursements. If you’re claiming a loss on an uninsured portion, records showing the policy’s coverage limits or deductible amount.
A timeline: a chronological record of the event, your discovery of the damage, insurance claim filings, repair work, and any communication with government agencies.

Photographs are particularly valuable. Before-and-after photos are often the single most persuasive piece of evidence in an audit. If you don’t have pre-casualty photos, home inventory videos, real estate listing photos, or even Google Street View screenshots from before the event can help establish what the property looked like.

1
Internal Revenue Service. Topic No. 515, Casualty, Disaster, and Theft Losses
2
Internal Revenue Service. Publication 547 – Casualties, Disasters, and Thefts
3
Office of the Law Revision Counsel. 26 U.S. Code 165 – Losses
4
Office of the Law Revision Counsel. 26 USC 165 – Losses
5
Internal Revenue Service. Instructions for Form 4684 – Casualties and Thefts
6
Internal Revenue Service. Instructions for Form 4684
7
Office of the Law Revision Counsel. 26 U.S. Code 1033 – Involuntary Conversions
8
Internal Revenue Service. Form 4684 – Casualties and Thefts
9
Federal Register. Election To Take Disaster Loss Deduction for Preceding Year