If you are a Real Estate Professional or sold your rental property during the year, you will need to indicate this on the tax return to allow your full loss amount. In the Schedule E, the last checkbox (Check here if you are a real estate professional or disposed of the property this year) will need to be marked to allow the loss amount.
To be considered a real estate professional, you must meet certain guidelines.
For more information, see What are the requirements to be considered a Real Estate Professional?