What this line means
The loss after reimbursement (line 9) minus $100. The IRS requires you to reduce each personal casualty or theft loss by $100 per event. If one hurricane damaged both your house and your car, that is one event — you subtract $100 once, not twice. If separate events caused losses (a theft in March and a flood in September), each event gets its own $100 reduction.
Does this apply to you?
- You had a personal-use property casualty or theft loss and are calculating the deductible amount
- You experienced one or more separate casualty events during the year
- You need to apply the per-event $100 floor before calculating total losses
Easy to overlook
The $100 reduction is per event, not per property A single storm that damages your house, car, and shed is one event. You subtract $100 once from the combined loss. But a burglary in June and a fire in November are two events, each with its own $100 reduction. Applying $100 per property instead of per event overstates the reduction for single-event losses involving multiple items. 1 IRS Publication 547 — Casualties, Disasters, and Thefts
This $100 floor is separate from the 10% AGI threshold on line 18 The $100 per-event reduction on line 10 is a preliminary step. After applying the $100 floor to each event, the total losses still face the 10% of AGI reduction on line 18. These are two separate hurdles, not alternatives. A filer with $5,000 in casualty losses first subtracts $100, then subtracts 10% of AGI — often eliminating most or all of the deduction for moderate-income filers. 2 IRS Form 4684 instructions — Line 10
Watch out for this
Forgetting to subtract the $100 at all. Line 10 is line 9 minus $100 (use zero if line 9 is $100 or less). Filers focused on the larger 10% AGI threshold sometimes skip this smaller reduction. The $100 is mandatory for every casualty or theft event before moving to the totals section.
Footnotes
-
IRS Publication 547, Casualties, Disasters, and Thefts, $100 Rule. https://www.irs.gov/pub/irs-pdf/p547.pdf ↩
-
IRS Form 4684 Instructions, Line 10. https://www.irs.gov/instructions/i4684 ↩