Timestamp conversion is a simple math but always so confusing. Googling “2084-01-01 12:40:10 kst to est” will almost instantly give you the result. But this can also be easily done from command line.

From in the command prompt:

$ TZ='<TARGET_TZ>' date --date='TZ="<ORIG_TZ>" 2049-01-01 00:00:00'

For example from Seoul time to Toronto time.

$ TZ='America/Toronto' date --date='TZ="Asia/Seoul" 2049-01-01 00:00:00'
Thu Dec 31 10:00:00 EST 2048

Warning!!! It is tempting to use timezone name abbreviations but using them might give you a wrong result:

$ TZ='EST' date --date='TZ="KST" 2049-01-01 00:00:00'                                                              
Thu Dec 31 19:00:00 EST 2048     !!! Wrong result

It seems only names that can be found in “/usr/share/zoneinfo” should be used.