The POSIX specification for find says: -mtime n The primary shall evaluate as true if the file modification time subtracted from the initialization time, divided by 86400 (with any remainder discarded), is n . Interestingly, the description of find does not further specify 'initialization time'. It is probably, though, the time when find is initialized (run). In the descriptions, wherever n is used as a primary argument, it shall be interpreted as a decimal integer optionally preceded by a plus ( '+' ) or minus-sign ( '-' ) sign, as follows: +n More than n . n Exactly n . -n Less than n . Transferring the content of a comment to this answer. You can write -mtime 6 or -mtime -6 or -mtime +6 : Using 6 without sign means "equal to 6 days old — so modified between 'now - 6 * 86400' and 'now - 7 * 86400'" (because fractional days are discarded). Using -6 means "l...