“My question is could I have not claimed that loss since it didn't benefit me and now carry them forward since I'm back in the U.S. and will have a use for the loss.Wondering if there is a difference between disallowed rental losses and choosing not to take those rrental losses.?”--->I guess It depends on the situation;however, as you rented out your primary residence for the whole year while you were in Canada,your residence is treated as rental property. Your rental losses’ be deducted against other income, probably subject to passive loss rules. Congress enacted legislation limiting the deduction of certain passive losses from other taxable income. Because the most common passive loss seen on tax returns is from ordinary real estate rental activities, many taxpayers with an investment in a real estate rental property are affected by these rules.In general, you can’t offset your passive losses against either active or portfolio income. Also, any tax credits derived from passive activities can only offset income taxes attributable to passive income. Any unused passive loses and crdits are carried over and may be used to offset your future passive income or taxes attributable to such incomer, respectively. REMEBER: your passive activity losses remaining when you dispose of your property MAY be used in full.