POSIX Timestamp Converter
A POSIX timestamp is technically the same as a Unix timestamp: the number of seconds elapsed since January 1, 1970, 00:00:00 UTC, as defined by the POSIX standard (IEEE Std 1003.1). The terms Unix time, epoch time, POSIX time, and Unix timestamp are all used interchangeably in practice, and they all refer to the same integer value representing the same moment in time.
POSIX (Portable Operating System Interface) is a family of standards that defines the API for Unix-like operating systems. The POSIX time specification is one of its most universally adopted components, forming the foundation for how time is represented in C, C++, Python, Ruby, Perl, and virtually every other language that runs on Unix-like systems.
POSIX time and leap seconds
One important nuance: POSIX time deliberately ignores leap seconds. Every day is treated as exactly 86,400 seconds, even on days when a leap second is inserted. This means POSIX timestamps are not a perfectly accurate representation of UTC — they're off by approximately 27 seconds as of 2024 (the number of leap seconds that have been added since 1972). For the vast majority of applications, this discrepancy is completely irrelevant. It only matters in extremely high-precision timing systems like financial trading platforms or scientific instrumentation.
POSIX timestamp in C
#include <time.h>
time_t now = time(NULL); // current POSIX timestamp
struct tm *utc = gmtime(&now); // convert to UTC struct
printf("%d-%02d-%02d
", utc->tm_year+1900, utc->tm_mon+1, utc->tm_mday);
Enter your POSIX timestamp in the converter above to see the corresponding date and time in any timezone.