f766d2e3_s_for_Organizing_Paper_Clutter__Why_
[0] Tax Documents [How Long?] 7 years [Why?] 
The IRS generally does not audit back farther than 7 years (as long as no fraud is suspected), so save all documentation (receipts, tax forms, annual income statements) that backs up the information on your tax return for only this long. Note that you can scan tax documents and save them on your computer. Save the returns themselves forever.
How To Organize Papers - Tips for Organizing Paper Clutter
Why?