Unix Timestamp: What It Is and How to Convert It

What Is a Unix Timestamp?

A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have elapsed since January 1, 1970, at 00:00:00 UTC. This single point in time, called the Unix epoch, serves as the reference point for timekeeping in most computer systems.

For example, the timestamp 1700000000 represents November 14, 2023, at 22:13:20 UTC. The timestamp 0 represents the epoch itself. Negative timestamps represent dates before 1970, so -86400 corresponds to December 31, 1969.

Unix timestamps are timezone-independent, making them ideal for storing, comparing, and transferring time data across systems that may operate in different time zones.

Why Developers Use Timestamps

Storage efficiency: A timestamp is a single integer, requiring minimal storage compared to formatted date strings. This matters in databases handling millions of records.

Comparison simplicity: To determine which of two events happened first, compare two integers. No date parsing or timezone conversion required.

Timezone neutrality: Timestamps represent a single moment in time regardless of location. The conversion to a local date and time happens only at the display layer, preventing confusion when systems in different time zones exchange data.

Arithmetic ease: Adding 86,400 to a timestamp advances it by exactly one day (86,400 seconds). Subtracting two timestamps gives the difference in seconds. These operations are trivial with integers but complex with formatted dates.

How to Convert

Timestamp to date: Divide the timestamp by 86,400 to get the number of days since the epoch, then calculate the date from January 1, 1970. In practice, programming languages handle this automatically. JavaScript uses new Date(timestamp * 1000) (JavaScript uses milliseconds). Python uses datetime.fromtimestamp(timestamp). PHP uses date(‘Y-m-d H:i:s’, timestamp).

Date to timestamp: Most languages provide functions to create a timestamp from a date. JavaScript: Math.floor(Date.now() / 1000). Python: int(datetime.now().timestamp()). PHP: time() or strtotime().

Current timestamp: As of early 2026, the current Unix timestamp is approximately 1,775,000,000. The timestamp increases by 1 every second, 86,400 per day, and about 31,536,000 per year.

The Year 2038 Problem

Unix timestamps stored as 32-bit signed integers can represent dates up to January 19, 2038, at 03:14:07 UTC. After that moment, the integer overflows and wraps to a negative number, which would be interpreted as December 1901. This is analogous to the Y2K problem.

Most modern systems use 64-bit integers for timestamps, which extend the range to billions of years into the future. However, legacy systems, embedded devices, and some database schemas still use 32-bit timestamps. Identifying and upgrading these systems is an ongoing effort in the software industry.

Common Pitfalls

Seconds vs. milliseconds: JavaScript and some APIs use milliseconds (13-digit timestamps like 1700000000000), while Unix convention uses seconds (10-digit timestamps like 1700000000). Confusing the two produces dates far in the future or the past.

Timezone handling: Timestamps are always UTC. When displaying to users, convert to the appropriate local timezone. Storing local times as timestamps without timezone information leads to ambiguity and bugs during daylight saving transitions.

Leap seconds: Unix timestamps technically do not account for leap seconds, meaning some real-world seconds are “repeated” in the timestamp count. For most applications this is irrelevant, but high-precision timekeeping systems must account for it.

Use the timestamp converter on CalcHub to convert between Unix timestamps and human-readable dates, or explore our developer tools for more utilities.

Convert Unix timestamps to dates and back with CalcHub’s developer tools.