strtotime Parse about any English textual datetime description into a Unix timestamp intstrtotime stringtime intnow The function expects to be given a string containing an English date format and will try to parse that format into a Unix timestamp relative to the timestamp given in now, or the current time if none is supplied. Upon failure, -1 is returned. Because strtotime behaves according to GNU date syntax, have a look at the GNU manual page titled Date Input Formats. Described there is valid syntax for the time parameter. ]]> ]]> The valid range of a timestamp is typically from Fri, 13 Dec 1901 20:45:54 GMT to Tue, 19 Jan 2038 03:14:07 GMT. (These are the dates that correspond to the minimum and maximum values for a 32-bit signed integer.) Additionally, not all platforms support negative timestamps, therefore your date range may be limited to no earlier than the Unix epoch. This means that e.g. dates prior to Jan 1, 1970 will not work on Windows, some Linux distributions, and a few other operating systems.