If you discover an error on your federal income tax return after you e-filed or mailed it, you may want or need to amend your return. Perhaps you are eligible for a deduction or credit and you missed it the first time?

Here are six key points to know when considering whether to file an amended federal income tax return.

1. Some errors don’t require amending.  Generally, you do not need to file an amended return to correct math errors. The IRS will automatically make that correction. Also, do not file an amended return because you forgot to attach tax forms such as W-2s or schedules. The IRS normally will send a request asking for those.
2. Timing is crucial. You must file Form 1040X within three years from the date you filed your original return or within two years from the date you paid the tax, whichever is later.  What if you are filing for an additional refund?  You should wait until after you have received your original refund before filing Form 1040X. You may cash the first check while waiting for any additional refund.
3. Amend each year separately.  If you are amending more than one tax return, prepare a separate 1040X for each year.  Mail each amended return in separate envelope to the appropriate IRS campus (they used to be called ‘IRS Service Centers’) for the area you live in. The 1040X instructions list the addresses for the campuses.
4. No electronic filing allowed.  Amended returns are only filed on paper, so even if you filed your original return electronically, you’ll have to amend on paper. Amended returns are prepared on Form 1040X. You must use this form whether you previously filed Form 1040, 1040A or 1040EZ.
5. Don’t forget penalties and interest.  If you owe additional 2011 tax, file Form 1040X and pay the tax before the due date to limit interest and penalty charges that could accrue on your account. Interest is charged on any tax not paid by the due date of the original return, without regard to extensions.  The IRS will compute the interest and send you a bill if you don’t include it. If the IRS thinks you owe penalties it will send you a notice, which you can either pay or contest.
6. State Income Taxes.  If you file an amended tax return with the IRS (or the IRS corrects your due to a math error), don’t forget that you will need to amend your State Income Tax return also.