What is a Unix Timestamp?
A Unix timestamp (also known as Epoch time, POSIX time, or Unix Epoch time) is a system for tracking time as a running total of seconds. It counts the number of seconds that have elapsed since January 1, 1970 at 00:00:00 UTC — a moment known as the “Unix Epoch.”
For example, the Unix timestamp 1700000000corresponds to November 14, 2023 at 22:13:20 UTC. Because it's a single number with no timezone or formatting ambiguity, Unix timestamps are the universal language of time in computing.
The Unix Epoch Explained
The Unix Epoch is the zero-point of Unix time: January 1, 1970 00:00:00 UTC. Every Unix timestamp is simply the number of seconds before or after this moment. Dates before the Epoch are represented as negative numbers.
This reference point was chosen by the creators of the Unix operating system at Bell Labs in the early 1970s. It was a round, recent date that kept timestamp values small enough to store in a 32-bit signed integer for decades to come.
Notable Unix Timestamps
| Event | Timestamp | Date (UTC) |
|---|---|---|
| Unix Epoch | 0 | Jan 1, 1970 00:00:00 |
| First Moon Landing | -14182940 | Jul 20, 1969 20:17:40 |
| Y2K | 946684800 | Jan 1, 2000 00:00:00 |
| 1 Billion Seconds | 1000000000 | Sep 9, 2001 01:46:40 |
| Max 32-bit (Y2038 Problem) | 2147483647 | Jan 19, 2038 03:14:07 |
| 2 Billion Seconds | 2000000000 | May 18, 2033 03:33:20 |
The Year 2038 Problem
Many older systems store Unix timestamps as a 32-bit signed integer, which has a maximum value of 2,147,483,647. This corresponds to January 19, 2038 at 03:14:07 UTC. After this moment, the value overflows and wraps around to a large negative number, causing the date to jump back to December 13, 1901.
Modern 64-bit systems are immune to this problem — a 64-bit signed integer can represent dates over 292 billion years into the future. However, embedded systems, databases, and file formats that still use 32-bit timestamps will need to be updated before 2038.
Common Use Cases
REST APIs & Webhooks
APIs use Unix timestamps in request/response payloads because they are timezone-independent and easy to parse in any language.
Databases
Storing timestamps as integers is compact, fast to index, and avoids timezone conversion issues across distributed systems.
Logging & Monitoring
Log entries use Unix timestamps for precise, sortable event ordering across servers in different timezones.
Caching & TTL
Cache expiration times are often set as Unix timestamps. Comparing the current time to the expiry timestamp is a simple integer comparison.
JWT & Auth Tokens
JSON Web Tokens use Unix timestamps for the iat (issued at), exp (expiration), and nbf (not before) claims.
Cron Jobs & Scheduling
Task schedulers convert cron expressions to Unix timestamps to determine the next execution time.
Seconds vs Milliseconds
| Feature | Seconds | Milliseconds |
|---|---|---|
| Digits (current era) | 10 digits | 13 digits |
| Precision | 1 second | 1 millisecond |
| Used by | Unix/Linux, PHP, Python, Ruby, C | JavaScript, Java, Dart |
| Example (now-ish) | 1700000000 | 1700000000000 |
Frequently Asked Questions
A Unix timestamp is the number of seconds (or milliseconds) that have elapsed since January 1, 1970 00:00:00 UTC, known as the Unix Epoch. It's a universal way to represent a point in time as a single number, avoiding timezone and formatting ambiguity.
10-digit timestamps represent seconds since the Epoch and are used by Unix/Linux, PHP, Python, and Ruby. 13-digit timestamps represent milliseconds and are used by JavaScript (Date.now()), Java (System.currentTimeMillis()), and many modern APIs. Our tool supports both formats.
The Year 2038 problem (Y2K38) occurs because many systems store Unix timestamps as 32-bit signed integers, which max out at 2,147,483,647 (January 19, 2038 03:14:07 UTC). After this moment, the value overflows to a negative number, causing dates to jump back to 1901. Modern 64-bit systems are not affected.
Yes. Negative Unix timestamps represent dates before the Epoch (January 1, 1970). For example, -86400 represents December 31, 1969. Most programming languages and databases support negative timestamps.
Absolutely. This tool runs 100% in your browser using client-side JavaScript. No data is sent to any server. Your timestamps and dates never leave your device.
In JavaScript: Math.floor(Date.now() / 1000). In Python: import time; int(time.time()). In PHP: time(). In Java: System.currentTimeMillis() / 1000. In Ruby: Time.now.to_i. In Go: time.Now().Unix(). In C: time(NULL).
Unix timestamps are always in UTC (Coordinated Universal Time). They represent an absolute point in time regardless of timezone. When you convert a timestamp to a human-readable date, your local timezone is applied for display purposes, but the underlying value is always UTC.
For 32-bit systems, the maximum is 2,147,483,647 (Jan 19, 2038). For 64-bit systems, the maximum is 9,223,372,036,854,775,807 which is over 292 billion years in the future — effectively unlimited for any practical purpose. JavaScript can safely handle timestamps up to the year 275,760.