A Unix timestamp is the number of seconds elapsed since 1 January 1970 00:00:00 UTC -- a moment known as the Unix epoch. It is the most universal way computers store and transmit time because it is a timezone-agnostic integer that requires no calendar logic to compare or sort. Most programming languages, databases, and APIs use Unix timestamps as their internal time representation.
Different systems chose different starting points and different units. Windows measures time in 100-nanosecond intervals since 1 January 1601. Apple's frameworks count seconds since 1 January 2001. GPS counts weeks and seconds since 6 January 1980. Excel counts days since 30 December 1899, with an intentional bug that treats 1900 as a leap year for Lotus 1-2-3 compatibility. Converting between these formats requires knowing the offset between each epoch and the Unix epoch, then accounting for differences in unit scale.
Paste any timestamp and get instant conversion to 17 formats: Unix seconds, Unix milliseconds, ISO 8601, RFC 2822, human readable, Windows FILETIME, Apple Cocoa time, Excel serial date, NTP timestamp, GPS timestamp, .NET DateTime ticks, WebKit timestamp, TAI, Julian Day Number, Modified Julian Date, Lilian Date, and Unix Day. The specialist tools handle JWT token decoding, cron expression parsing, relative time expressions, and batch log normalisation. All conversions happen client-side -- nothing is sent to a server.