What this line means
The total of all personal casualty and theft losses after the $100 per-event reduction. This combines the line 10 amounts from all separate casualty events during the year. This total is then compared to casualty gains (line 14) and ultimately reduced by 10% of your AGI to arrive at the deductible amount.
Does this apply to you?
- You had one or more casualty or theft losses on personal-use property during the year
- You completed the per-property calculations in Section A and need to total all losses
- You need to determine your combined losses before the AGI threshold reduction
Easy to overlook
Losses from multiple federally declared disasters are combined If two separate federally declared disasters affected you in the same year — for example, a hurricane in the fall and a wildfire in the summer — the losses from both events are totaled here. Each event has its own $100 reduction applied already, but the 10% AGI reduction on line 18 applies only once to the combined total. 1 IRS Publication 547 — Casualties, Disasters, and Thefts
Prior-year disaster losses can be claimed on the prior year’s return For federally declared disasters, you can elect to claim the loss on the prior year’s return instead of the current year’s. This is useful if your AGI was lower in the prior year, making the 10% AGI threshold easier to clear. The election is made by filing an amended return for the prior year. 2 IRS Form 4684 instructions — Lines 15-18
Watch out for this
Adding losses from non-qualifying events. After 2017, personal casualty losses are deductible only if they result from a federally declared disaster. A theft loss or a casualty from a non-declared event does not qualify and should not be included in line 15. Including non-qualifying losses inflates your deduction and triggers an IRS adjustment.
Footnotes
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IRS Publication 547, Casualties, Disasters, and Thefts, Federally Declared Disasters. https://www.irs.gov/pub/irs-pdf/p547.pdf ↩
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IRS Form 4684 Instructions, Disaster Loss Election. https://www.irs.gov/instructions/i4684 ↩