What Is Unix Time? Epoch Timestamps Explained

The epoch is a starting point; Unix time is a count

An epoch is the reference instant used by a timekeeping system. The Unix epoch is midnight UTC at the start of January 1, 1970. Unix time, also called POSIX time, expresses an instant as a count of seconds relative to that origin. In everyday programming, “epoch time” usually means the timestamp rather than the starting instant itself.

Unix time does not count leap seconds. Its calendar model treats an ordinary day as 86,400 seconds. This makes it convenient for storing events and comparing dates across applications, but it should not be confused with a scientific time scale that continuously counts every physical second.

Read a timestamp with a few concrete examples

Zero means the epoch itself. Adding 86,400 advances by one day in the Unix calendar. A negative value refers to an instant before 1970: minus one is the final second of December 31, 1969. These examples use seconds, not milliseconds.

One timestamp can have several local displays

A Unix timestamp does not carry a time zone. For example, 1767225600 is both January 1, 2026 at 00:00 UTC and January 1 at 05:30 in India. Displaying a different local time does not change the stored number. Include the zone when sharing a human-readable date so another person can identify the same instant.

The reverse conversion needs more context. A date such as 2026-01-01 00:00:00 means different instants in UTC and local time. In places observing daylight saving time, some local clock times do not exist, while others occur twice. UTC input avoids that ambiguity. This converter rejects skipped local times and selects the earlier occurrence of a repeated local time.

Convert epoch time to a date, or a date to epoch time

In the epoch-to-date tool, enter the number and select its unit. Use Seconds for the examples above. Convert to see UTC, your browser’s local time, and an ISO 8601 result. If an unfamiliar value resolves to a surprising year, check the unit before adjusting the time zone.

For date-to-epoch conversion, choose the date input format and UTC/GMT or local time in Preferences. Enter the date and a 24-hour clock time, then convert. The result includes equivalent values in seconds, milliseconds, microseconds, and nanoseconds. Use the ISO result when you need to inspect fractional seconds.

The Year 2038 limit belongs to a particular storage type

A signed 32-bit seconds counter can store at most 2147483647. That value corresponds to January 19, 2038 at 03:14:07 UTC; the following second exceeds its range. The problem concerns systems using that representation, rather than Unix time as a concept. Systems with sufficiently wide time types can represent later dates. This converter is not limited to a signed 32-bit seconds counter.