Casualty losses are deductible in the year you sustain the loss, which is generally in the year the casualty occurred. You have not sustained a loss if you have a reasonable prospect of recovery through a claim for reimbursement. If you have a casualty loss from a federally declared disaster that occurred in an area warranting public or individual assistance (or both), you can choose to treat the casualty loss as having occurred in the year immediately preceding the tax year in which you sustained the disaster loss, and you can deduct the loss on your return or amended return for that preceding tax year.

Casualty losses are part of the itemized deductions.  There is a $100 deduction for a casualty and then the balance after any reimbursement that is in excess of 10% of your adjusted gross income is allowed as a deduction.  This result is combined with other itemized deductions.