There is only one file type that uses the .T13 extension:
H&R Block 2013 Tax Return
Tax return created with H&R Block 2013 tax software or exported from H&R Block online; contains U.S. federal tax forms for 2013; may also include state tax forms for a specific state; stores personal data and tax information entered by the user.
Completed tax returns can be filed electronically directly from the software. They can also printed and mailed to the appropriate tax authorities.
NOTE: Previous versions of H&R Block's tax return software were called "At Home." Tax returns created with At Home 2012 were created with a .T12 file extension.
Updated: April 10, 2015