I have the following time : 2010-01-25 03:13:34.384 - GMT Time Zone 2010-01-25 11:13:34.384 - My Local I wish to convert to timestamp in ms. However, since I only obtain local time string from caller "2010-01-25 11:13:34.384" If I do it this way : // ts is "2010-01-25 11:13:34.384" (My Local) boost::posix_time::ptime t(boost::posix_time::time_from_string(ts)); boost::posix_time::ptime end(boost::gregorian::date(1970,1,1)); boost::posix_time::time_duration dur = t - end; // epoch is 1264418014384 // 2010-01-25 11:13:34.384 (GMT) -- But I want 2010-01-25 03:13:34.384 // 2010-01-25 19:13:34.384 (My Local) -- But I want 2010-01-25 11:13:34.384 long long epoch = dur.total_milliseconds(); Is there any way to tell boost::posix_time, that the ts string which it receives, is belong to My Local timezone?