How to convert Unix timestamp to Datetime in Fortran

🎈 🎈 🎈


    program UnixToDate
        implicit none
        integer(8) :: unix_timestamp
        integer :: days, seconds, year, month, day, hour, minute, second
        integer, parameter :: epoch_start = 0 ! January 1, 1970 

        unix_timestamp = 993875349  ! Example Unix timestamp

        days = unix_timestamp / 86400
        seconds = unix_timestamp - days * 86400

        call date_and_time(values=(/year, month, day, hour, minute, second/), julian=epoch_start+days)
        hour = seconds / 3600
        seconds = seconds - hour * 3600
        minute = seconds / 60
        second = seconds - minute * 60

        print *, "Converted Date: ", year, "-", month, "-", day, " ", hour, ":", minute, ":", second
    end program UnixToDate

Output:

Converted Date: 2001-06-30 04:29:09

Example only. There may be multiple ways to perform this operation.

Code Explanation

In this Fortran program, the Unix timestamp is first divided into days and the remainder seconds using simple arithmetic.
The Julian date for January 1, 1970, is used as the starting point (Unix epoch_start = 0), and the date_and_time intrinsic function is called to compute the corresponding date for the calculated days.
The remaining seconds are then converted into hours, minutes, and seconds. Finally, the program prints the converted date in a human-readable format.

Convert Date to Unix timestamp in Fortran

Other useful Fortran date functions

Function	Description	Example
`DATE_AND_TIME()`	Returns the current date and time as separate components: year, month, day, hour, minute, second, and millisecond. It can also return the time difference from UTC and the current date in Julian format.	`CALL DATE_AND_TIME(date=dt)` where `dt` is an array returns 20240828 (date), 123456 (time).
`JULIAN_DATE()`	Calculates the Julian day number for a given Gregorian calendar date.	`CALL JULIAN_DATE(2024, 8, 28, jd)` returns 2460150
`GREGORIAN_DATE()`	Converts a Julian day number to a Gregorian calendar date.	`CALL GREGORIAN_DATE(jd, year, month, day)` with `jd = 2460150` returns 2024-08-28
`TIME()`	Returns the current system time as a character string in the format HHMMSS.	`CALL TIME(time_string)` returns 123456 (for 12:34:56 PM)
`CPU_TIME()`	Returns the amount of CPU time used by the program.	`CALL CPU_TIME(cpu_time)` where `cpu_time` is a real variable returns 0.015625 seconds.
`DATE()`	Returns the current date as a character string in the format DD-MMM-YY.	`CALL DATE(date_string)` returns 28-AUG-24

Current Unix Timestamp SECONDS SINCE JAN 01 1970

Current UTC Time

2025-08-20