What is a Unix timestamp and how does it work?

A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC (the Unix epoch). For example, timestamp 1609459200 represents January 1, 2021, 00:00:00 UTC. This standard provides a simple, timezone-independent way to represent dates and times as a single number, making it easy to store in databases, compare dates, and calculate time differences. Unix timestamps are used universally across programming languages, databases, and APIs.

How do I convert a Unix timestamp to a readable date?

Simply paste the Unix timestamp (like 1609459200) into the converter and it will display the corresponding date and time in human-readable format (like 'January 1, 2021, 00:00:00 UTC'). You can choose your timezone to see the date in local time. The converter automatically detects whether your timestamp is in seconds (10 digits) or milliseconds (13 digits). Most programming languages have built-in functions for this conversion: JavaScript uses new Date(timestamp * 1000), Python uses datetime.fromtimestamp(timestamp), PHP uses date('Y-m-d H:i:s', timestamp).

What's the difference between seconds and milliseconds timestamps?

Traditional Unix timestamps count seconds since the epoch (10 digits, like 1609459200). Milliseconds timestamps count milliseconds since the epoch (13 digits, like 1609459200000). Milliseconds provide greater precision, useful for high-frequency events like stock trades, server logs, or performance monitoring. JavaScript's Date.now() returns milliseconds, while most Unix systems and databases use seconds. To convert between them: multiply seconds by 1000 to get milliseconds, or divide milliseconds by 1000 to get seconds. Our converter automatically detects which format you're using based on digit count.

How do I get the current Unix timestamp?

Our tool displays the current Unix timestamp in real-time at the top of the page. In programming: JavaScript uses Math.floor(Date.now() / 1000) for seconds or Date.now() for milliseconds, Python uses int(time.time()), PHP uses time(), Java uses System.currentTimeMillis() / 1000, and shell scripts use date +%s. The current timestamp is useful for timestamping database records, logging events, measuring code execution time, generating unique IDs, or implementing rate limiting in APIs.

How does the converter handle different timezones?

Unix timestamps are always in UTC (Coordinated Universal Time) by definition—they represent a specific moment in time regardless of timezone. However, when displaying timestamps as readable dates, timezone matters. Our converter lets you select any timezone to see how that timestamp translates to local time. For example, timestamp 1609459200 is '2021-01-01 00:00:00 UTC' but '2020-12-31 16:00:00 PST' (8 hours behind). When converting dates to timestamps, the tool considers your selected timezone before calculating the UTC timestamp value. Always store timestamps in UTC in databases for consistency.

What is the Year 2038 problem (Y2K38)?

The Year 2038 problem affects 32-bit systems that store Unix timestamps as signed integers. The maximum value for a 32-bit signed integer is 2,147,483,647, which represents Tuesday, January 19, 2038, 03:14:07 UTC. After this date, the timestamp will overflow and wrap to negative values, potentially causing system failures. Modern 64-bit systems don't have this problem—they can represent dates billions of years into the future. Most operating systems, databases, and programming languages have migrated to 64-bit timestamps. If you're working with legacy systems, plan to upgrade before 2038!

Can Unix timestamps represent dates before 1970?

Yes! Negative Unix timestamps represent dates before the epoch (January 1, 1970). For example, -86400 represents December 31, 1969, 00:00:00 UTC (one day before the epoch). This is useful for historical dates, birthdates, or any events before 1970. Most modern systems support negative timestamps without issues. However, some older systems or languages may have limitations with negative values. The theoretical minimum for 32-bit signed timestamps is December 13, 1901, but 64-bit systems can represent dates billions of years in the past.

Why do APIs and databases use Unix timestamps?

Unix timestamps offer several advantages for APIs and databases: they're timezone-independent (always UTC), easy to compare mathematically (just subtract to get duration), sortable as numbers, compact to store (4-8 bytes vs formatted date strings), language-agnostic (universally understood), and free from date format ambiguity (is 01/02/2021 January 2 or February 1?). They're also fast to process—numeric comparisons are cheaper than string parsing. When exchanging data between systems, timestamps eliminate confusion about date formats, timezones, and locale differences.

How accurate are Unix timestamps with leap seconds?

Unix time doesn't account for leap seconds—it assumes every day has exactly 86,400 seconds. Leap seconds are occasionally added to UTC to account for Earth's irregular rotation, but Unix timestamps skip them. This means there's a small discrepancy (currently about 37 seconds) between strict UTC and Unix time. For most applications, this difference is negligible and acceptable. High-precision scientific applications might use TAI (International Atomic Time) instead. The advantage of ignoring leap seconds is that Unix time is monotonic and predictable, making it easier for software to handle.

How do I convert Unix timestamps in different programming languages?

Common conversions: JavaScript: new Date(timestamp * 1000).toLocaleString() for seconds, new Date(timestamp).toLocaleString() for milliseconds. Python: datetime.fromtimestamp(timestamp) or datetime.utcfromtimestamp(timestamp). PHP: date('Y-m-d H:i:s', timestamp). Java: new Date(timestamp * 1000L) for seconds. MySQL: FROM_UNIXTIME(timestamp). PostgreSQL: to_timestamp(timestamp). Excel: equals (timestamp / 86400) + 25569 then format as date. Each language has built-in functions making conversion straightforward. Always check if your timestamp is in seconds or milliseconds first!