When a casualty or disaster loss is larger than your income for the year it happened, the unused portion does not vanish. The casualty and disaster loss deduction carryover rules let you convert that excess into a net operating loss, then either carry it back one year for an immediate refund or carry it forward indefinitely against future taxable income. Which route you choose, and how you file for it, controls how quickly the loss turns into cash and how much of it you eventually recover.
How a Disaster Loss Becomes a Carryover
The carryover only exists if your allowable deductions for the disaster year exceed your gross income. Under 26 U.S.C. § 172, that excess is a net operating loss, computed with certain modifications.1Office of the Law Revision Counsel. 26 USC 172 – Net Operating Loss Deduction You do not need to run a business for this to apply. A personal disaster loss that overwhelms your wages and other income creates an NOL just the same.2Internal Revenue Service. Publication 547 (2025), Casualties, Disasters, and Thefts
To arrive at the number you actually carry, you first apply the disaster loss against the disaster year’s income. Non-business deductions that exceed non-business income are then stripped out of the calculation. Whatever negative amount remains is your NOL: the figure that moves to another tax year.
Before this step you need a properly computed loss on Form 4684. That means basis versus fair market value decline (whichever is smaller), reduced by insurance you received or reasonably expect to receive, and then reduced again by the $100 or $500 per-casualty floor and, for standard federally declared disasters, 10% of adjusted gross income. Business and income-producing property losses skip the floor and the AGI reduction. If your policy would have covered the damage but you never filed a claim, the IRS will not treat the unclaimed portion as a deductible loss.2Internal Revenue Service. Publication 547 (2025), Casualties, Disasters, and Thefts
Carrying the Loss Back to the Prior Year
The fastest path to money after a disaster is the election under 26 U.S.C. § 165(i). It lets you treat the loss as though it happened in the tax year immediately before the disaster year.3Office of the Law Revision Counsel. 26 USC 165 – Losses A hurricane in 2026 becomes a deduction on your 2025 return, and the resulting refund arrives during the recovery period rather than after you file for 2026.
The election must be made within six months after the regular due date (without extensions) for filing the disaster-year return.4eCFR. 26 CFR 1.165-11 – Election To Take Disaster Loss Deduction for Preceding Year For a calendar-year individual with a 2026 loss, that deadline is October 15, 2027. You make the election by completing Section D of Form 4684 and attaching it to the original or amended prior-year return.5Internal Revenue Service. Instructions for Form 4684 By electing, you agree not to deduct the same loss on the disaster year return.
If the prior year’s income cannot absorb the entire loss, the leftover follows the carryforward rules below.
Carrying the Loss Forward
Whatever the current year and any elected carryback year cannot absorb rolls forward. Under current law, NOLs carry forward indefinitely with no expiration date.1Office of the Law Revision Counsel. 26 USC 172 – Net Operating Loss Deduction
In each future year, the NOL deduction is generally capped at 80% of that year’s taxable income. The remaining 20% stays taxable even while you are still working through the carryforward. A very large loss may take several years to burn off, but as long as you have future taxable income, it will eventually be used.
You can also waive the carryback and apply the loss only to future years. This can pay off if you expect to be in a higher bracket going forward, because the same deduction will offset income taxed at a higher rate. The tradeoff is finality: the waiver, once made, is irrevocable for that tax year.1Office of the Law Revision Counsel. 26 USC 172 – Net Operating Loss Deduction You must make the waiver election by the due date, including extensions, for filing the return for the year the NOL arose.
Which Forms to File and When
Three forms carry a disaster loss through the carryover process, and each has its own clock.
Form 4684
Every casualty claim starts on Form 4684, Casualties and Thefts. Section A handles personal-use property; Section B handles business or income-producing property.6Internal Revenue Service. Instructions for Form 4684 If you are making the § 165(i) election to deduct the loss in the preceding year, Section D is where the election itself lives. Attach the completed form to the return for the year in which you are claiming the deduction.5Internal Revenue Service. Instructions for Form 4684
Form 1045 for a Tentative Refund
If the loss creates an NOL and you want the carryback refund quickly, file Form 1045, Application for Tentative Refund. It must be filed within one year after the end of the year the NOL arose. The IRS is required to process it and issue a tentative refund within 90 days.7Internal Revenue Service. Instructions for Form 1045
Form 1040-X as the Alternative
If you are using the § 165(i) election to claim the loss on the preceding year’s return, the vehicle is Form 1040-X, an amended return for that prior year. The filing deadline mirrors the election deadline: six months after the regular due date (without extensions) for the disaster-year return. Processing generally takes 16 weeks or more, longer than Form 1045.8Internal Revenue Service. Instructions for Form 1040-X
Most standard disaster loss returns can be e-filed, but some complex carryback claims must go on paper. If you mail a paper return, confirm the current IRS processing center address for your state.
Mistakes That Break a Carryover
A loss that gets disallowed or reduced does more than shrink your refund. It can trigger a 20% accuracy-related penalty under 26 U.S.C. § 6662 when the underpayment stems from negligence, a substantial understatement, or a substantial valuation misstatement.9Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments For individuals, an understatement is “substantial” if it exceeds the greater of 10% of the tax that should have been shown or $5,000.
The errors that most often cost taxpayers their carryover:
- Missing the § 165(i) six-month election window, which forfeits the carryback entirely.
- Waiving the carryback and later regretting it, since the waiver cannot be revoked.
- Deducting the full loss when insurance would have covered part of it but no claim was filed.
- Using replacement cost in place of fair market value, which the IRS will roll back to FMV.
- Failing to subtract expected reimbursements in the year of the loss, even if the check arrives later. If the eventual payout is smaller than expected, you adjust in the year you find that out.
- Forgetting the $100 or $500 per-casualty floor, or the 10% of AGI reduction where it applies.
- Claiming the loss in the wrong year without a valid election covering that choice.
Substantiation is where audits are won or lost. The IRS expects records of ownership, the casualty event, pre- and post-loss fair market value, adjusted basis, and the status of any insurance claim.2Internal Revenue Service. Publication 547 (2025), Casualties, Disasters, and Thefts Where original records were destroyed in the event itself, the IRS accepts reconstructed records supported by bank statements, credit card records, prior tax returns, and photographs.10Internal Revenue Service. Reconstructing Records After a Natural Disaster or Casualty Loss For a carryback that spans two tax years and possibly a Form 1045 filing, professional help typically runs $200 to $1,500 and is usually cheaper than the penalty exposure on a mishandled claim.