If you file your taxes electronically, you have to select a five-digit PIN to authorize your tax return's submission. You can no longer use the paper form 8543 for this purpose. To select your PIN, you must know one of the following items from your previous year's tax return: the adjusted gross income, or AGI; the PIN you chose the previous year to authorize your return; or a PIN from the IRS for the year you're filing your taxes. Once you verify your identify through one of these means, you can choose any five-digit number except for all zeroes.

Finding Your AGI

If you're over the age of 16, you can file an electronic tax return. Otherwise, you must file a paper return. To find your prior year's AGI, locate a paper or electronic copy of your tax return from the prior year. You can find the AGI by going to the line where the AGI is listed on the appropriate tax form. If you filed a 1040, it is on line 38. It’s on line 21 of the 1040A and line 4 of the 1040EZ. If you corrected or amended your previous return, you still need to use the figure that was originally accepted by the Internal Revenue Service.

Contacting the IRS

If you can't find or access your tax return from the previous year, you can get a PIN by contacting the IRS Electronic Filing PIN system. This is located at IRS.gov, the IRS website. You also can call 1-866-704-7388 with a touch-tone phone for the IRS automated phone PIN retrieval service. If you prefer a live representative, you can call 1-800-829-1040 and talk with a customer service representative from the IRS. Either way, you'll need to provide the following information to receive your PIN: Social Security Number, first and last name, date of birth, filing status and the mailing address you used on your last tax return.

First-Year and Joint Filers

If this is your first year to file a tax return, or you didn't do so in the previous year, or you filed with an individual taxpayer ID number instead of a Social Security number, you'll select "I am a first-time filer" or "I did NOT file a (enter year you did not file) tax return" from the menu on the "E-Filing -- Prior Year Information" screen. If you're married and only one spouse previously filed, enter the AGI for the one who filed and the value of "0" for the non-filing spouse. If you filed jointly, enter the joint AGI. Don’t split it up for each spouse.

Changing Status

If your filing status changed from married filing jointly to another status during the year, each spouse still uses the joint AGI from the previous tax year. This also applies if you were married to a different spouse. You'll use last year's joint AGI even though you filed with a different spouse. If you changed from another status to married filing jointly, each taxpayer uses prior AGI from the previous filing. In other words, this data line is about pinpointing your identity, not financial data. No matter your current filing status, you need to verify your identity by referencing the AGI associated with your name from the previous tax year.