Casualty Loss - When your loss is deductible

You can generally deduct a casualty or disaster area loss only in the tax year in which the casualty or disaster occurred. You can generally deduct a theft loss only in the year you discovered your property was stolen. However, you can choose to deduct disaster area losses on your return for the year immediately before the year of the disaster if the President has declared your area a federal disaster area.
For details, see Disaster Area Losses in Publication 547.