The standard difference operator (-) returns day-based results for both date, timestamp and timestamp with time zone (the former returns days as int, the latter two return day-based intervals): From the day-based intervals you can extract days with the extract() function: select current_date - '2017-01-01', extract(day from now()::timestamp - '2017-01-01 00:00:00'), extract(day from now() - '2017-01-01 00:00:00Z');

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interval values can be written using the following verbose syntax: [@] quantity unit [quantity unit...] [direction] where quantity is a number (possibly signed); unit is microsecond, millisecond, second, minute, hour, day, week, month, year, decade, century, millennium, or abbreviations or plurals of these units