The Last Name field doesn't accept more than 20 characters.

[JohnB5677]

The IRS checks the first four letters of the last name to get a match.  You can post as much of your name as you can and leave the last letters off.

This is all based on your Social Security Number.  If you have a Hyphenated name you may have to check your Social Security Card, or you can contact The Social Security Administration at   1-800-772-1213 to confirm what they have on file.