if you're referring to your personal residence a loss isn't deductible. if there's a gain you should be able to claim an exemption - up to $500,000 providing the rules are met. if it's rental property any loss on the sale would be deductible while gain would be taxable with the portion of any gain up to the amount of depreciation that should have been taken taxed as 1250 recapture which may have a higher rate than long-term capital gains.
regardless of what type of property, no loss is allowed until sold.
