This Unix Day calculator shows how many days have passed since midnight UTC on January 1, 1970, also known as the Unix Epoch.
What is Unix time?
Unix time (also called POSIX time or Epoch time) counts seconds since January 1, 1970 00:00:00 UTC (POSIX definition). This calculator shows the day equivalent. The system was chosen by early Unix developers as a convenient "recent" date, and it has become the standard for computers worldwide.
You have probably seen Unix timestamps in URLs, log files, or database records. They look like large integers... for example 1735689600 for January 1, 2025. Dividing by 86,400 (seconds per day) gives the Unix day number.
The Year 2038 problem
32-bit systems store Unix time as a signed integer, which will overflow on January 19, 2038 at 03:14:07 UTC. This is similar to the Y2K bug, but for Unix systems. Most modern systems now use 64-bit timestamps, pushing the problem 292 billion years into the future... I'll be sure to update as we get closer.
Related calculators
- Unix Timestamp Converter - Convert seconds to dates
- Day Number Calculator - Days since Year 1
- Excel Date Serial Calculator - Spreadsheet dates
