you didn't take depreciation on the property. the IRS treats this as the adoption of an incorrect method of accounting, which may only be corrected by filing Form 3115, not amending prior years. This allows you to catch up on all the depreciation you missed without having to amend your previous returns. It's considered an automatic change, so the IRS generally grants these requests without much scrutiny. The form lets you take what's called a "Section 481(a) adjustment" that essentially gives you all the depreciation deductions you missed in one lump sum on your next return. The best part is you don't have to file amended returns for each year, which saves a lot of hassle.
