The Fair Market Value Before can be derived from an appraisal if you had one done within a short time before the hurricane.If not, you could ask a local realtor to do an estimated Fair Market Value.
It may not matter much if your Fair Market Value before was below the original purchase price. There is also a calculation done using the original purchase price of the house plus improvements and if the difference between that and Fair Market Value after is less than the difference between FMV before an FMV after, the smaller of the two differences is used to calculate the loss.
The after value wold be the value before you fixed or repaired the damage. In a federally declared disaster zone, you can use the cost of repairs to subtract from the FMV before the disaster to arrive at the FMV after, if the repairs are completed and paid for,.
