As a general rule, the longer you keep your tax documents, the better, however, the IRS has specific regulations regarding the length of time for which a taxpayer is required to keep his or her tax documents.

If you owe additional taxes, you must keep records for 3 years from the date of filing of the original or amended return, whichever is later unless the following conditions apply:

1) You do not report income subject to reporting and it is more than 25% of the total gross income shown on your tax return.  Keep records for 6 years.
2) The IRS can claim or prove that you have filed a fraudulent return.  Keep records indefinitely.
3) You do not file a return.  Keep records indefinitely.
4) You file a claim for credit or refund after you file your return.  Keep records for 3 years from the date you filed your original return or 2 years from the date you paid the tax, whichever is later.
5) You file a claim for a loss from worthless securities or bad debt.  Keep records for 7 years.
6) Keep all employment tax records (such as W-2's) for at least 4 years after the date that the tax becomes due or is paid, whichever is later.
7) Keep all records related to depreciable property for 3 years after the tax returns are filed for the year in which the property is disposed of.