Your theft loss is deductible if you are itemizing, and a subject to reduce loss by $100, and further to 10% of AGI. If you just missing property it’s not enough for deduction, theft needs to be proved!
In order to prove theft, one have to file a police report and attach it to tax return. Also police report needs to have detailed evidence of a break-in and list any witnesses.
Theft loss is deductible in the year its discovered, but not occurred, unless it all happened in the same year. If insurance is paying back for the lost items, then no deduction allowed. If taxpayer reimbursed only partially for the loss, then difference is deductible. If insurance reimburse taxpayer after theft-loss deduction is taken, taxpayer must add this payment back to the income on the tax return in a year reimbursement was received.
Computer fraud such as bank fraud, credit card theft, the “Nigerian” email scams, cyberextortion and ransomware, reimbursed monetary losses may be deductible as well.