An FTN file is a source code file written in Fortran, a programming language often used for numerical computation. It is saved in a plain text format and may be opened and edited with any text editor. FTN files may store code for an entire program or a program module.

FTN file open in Microsoft Visual Studio Code 1.33 You will most likely only encounter an FTN source code file if you are a scientific programmer. While FTN files can be opened and edited with any text editor, programmers typically edit FTN files with source code editors that provide Fortran syntax capabilities, such as Photran, Apple Xcode, and Bare Bones TextWrangler. After modifying FTN files, programmers compile the source code with a Fortran compiler, which translates it to machine code that can run on a computer as a program. Some examples of Fortran compilers include Absoft Pro Fortran and Intel Parallel Studio XE. NOTE: The .ftn file extension is shorthand for Fortran. Other files that store Fortran source code include .F, .F90, and .FOR files.