Hello, i think that i've found bug in date time library or maybe i made something wrog. SAMPLE CODE: #include <boost/date_time/posix_time/posix_time.hpp> #include <iostream> using namespace boost::posix_time; int main( int argc, char** argv ) { time_t t = time( 0 ); std::cout << "time_t: " << ctime( &t ) << std::endl; struct tm* t2 = localtime( &t ); std::cout << "struct tm: " << asctime( t2 ) << std::endl; ptime t3 = from_time_t( t ); std::cout << "ptime from time_t: " << to_simple_string( t3 ) << std::endl; ptime t4 = ptime_from_tm( *t2 ); std::cout << "ptime from tm: " << to_simple_string( t4 ) << std::endl; return 0; } OUTPUT: time_t: Fri May 1 14:22:01 2009 struct tm: Fri May 1 14:22:01 2009 ptime from time_t: 2009-May-01 12:22:01 // incorrect result ptime from tm: 2009-May-01 14:22:01