What is a Unix Timestamp?
A Unix timestamp, also known as Epoch time or POSIX time, represents the number of seconds that have elapsed since January 1, 1970, at 00:00:00 UTC. This date is known as the Unix Epoch, and it serves as the reference point for time measurement in Unix-like operating systems and many programming languages.
Unix timestamps are stored as simple integers, making them compact, efficient to store, and easy to perform arithmetic operations on. They’re timezone-agnostic at their core—a timestamp represents the same moment in time regardless of where you are in the world.
Understanding Timestamp Formats
Unix Timestamp (Seconds)
The traditional Unix timestamp measures time in whole seconds since the epoch. For example, 1702051200 represents December 8, 2024, at 15:00:00 UTC. This format is commonly used in system logs, databases, and older APIs.
Unix Timestamp (Milliseconds)
Many modern systems, especially JavaScript and Java, use milliseconds for greater precision. The same moment would be represented as 1702051200000. When you see a 13-digit number, it’s almost certainly a millisecond timestamp.
ISO 8601 Format
ISO 8601 is the international standard for date and time representation. An ISO 8601 timestamp looks like 2024-12-08T15:00:00.000Z, where T separates the date and time, and Z indicates UTC. This format is human-readable while remaining unambiguous and sortable.
RFC 2822 Format
Used primarily in email headers and HTTP protocols, RFC 2822 dates look like Sun, 08 Dec 2024 15:00:00 +0000. This format includes the day of the week and timezone offset, making it easy for humans to read.
How to Use This Tool
Timestamp to Date: Enter a Unix timestamp (in seconds or milliseconds) in the input field. The tool auto-detects the format and converts it to multiple readable formats in your selected timezone.
Date to Timestamp: Switch to the Date → Timestamp mode, use the date and time pickers to select your desired moment, and convert it to Unix timestamps in both seconds and milliseconds.
Quick Presets: Use the preset buttons to quickly load common timestamps like “Now,” “Start of Today,” or “7 Days Ago.”
Timezone Conversion: Select any timezone from the dropdown to see how the same moment appears in different parts of the world. The live clock also updates to show the current time in your selected timezone.
Common Use Cases
API Development
Many REST APIs use Unix timestamps for date fields. When debugging API responses or constructing requests, you’ll frequently need to convert between human-readable dates and timestamps.
Database Queries
SQL databases often store dates as timestamps. Converting between formats is essential when writing queries or analyzing data exports.
Log Analysis
Server logs typically record events with Unix timestamps. Converting these to readable dates helps when investigating issues or analyzing patterns over time.
Scheduling Systems
When building scheduling features, you’ll work with timestamps to calculate durations, set expiration times, and handle timezone-aware scheduling.
Data Synchronization
In distributed systems, timestamps help determine the order of events and resolve conflicts when synchronizing data across servers.
Timezone Considerations
Time zones add complexity to timestamp handling. While Unix timestamps are inherently UTC-based, displaying them to users requires timezone conversion.
UTC (Coordinated Universal Time) is the primary time standard. It doesn’t observe daylight saving time and serves as the reference for all other timezones.
Local Time varies by geographic location. The same timestamp represents different wall-clock times depending on where you are. New York (EST/EDT) is typically 5 hours behind UTC, while India (IST) is 5.5 hours ahead.
Daylight Saving Time (DST) causes many timezones to shift by one hour twice a year. This can cause confusion when comparing timestamps across DST transitions.
Best Practices for Timestamp Handling
Store in UTC: Always store timestamps in UTC format in your databases. Convert to local time only for display purposes.
Be Explicit: When exchanging dates between systems, include timezone information. ISO 8601 with timezone offset is ideal.
Handle Milliseconds: If you need sub-second precision, use millisecond timestamps. But be aware that some systems truncate to seconds.
Validate Input: Always validate timestamp input. Very large or very small numbers might indicate seconds vs. milliseconds confusion.
Consider the Year 2038 Problem: 32-bit systems storing seconds as signed integers will overflow on January 19, 2038. Use 64-bit integers for future-proof timestamp storage.
Common Timestamp Calculations
One hour in seconds: 3,600 One day in seconds: 86,400 One week in seconds: 604,800 One year (approximately): 31,536,000
These values are useful for adding or subtracting time periods from timestamps.
Frequently Asked Questions
What’s the difference between Unix timestamp and Epoch time?
They’re the same thing. “Unix timestamp,” “Epoch time,” “POSIX time,” and “Unix time” all refer to seconds since January 1, 1970 UTC.
How do I know if a timestamp is in seconds or milliseconds?
Count the digits. Timestamps in seconds are typically 10 digits (until 2286), while millisecond timestamps are 13 digits. Our tool auto-detects this for you.
Why do some systems use negative timestamps?
Negative Unix timestamps represent dates before January 1, 1970. For example, -86400 represents December 31, 1969.
What happens after the year 2038?
On 32-bit systems storing timestamps as signed integers, the maximum value (2,147,483,647) corresponds to January 19, 2038. After this, the value overflows. Modern 64-bit systems handle dates far into the future.
How accurate are Unix timestamps?
Standard Unix timestamps have one-second accuracy. For greater precision, use millisecond timestamps or specialized high-resolution time functions.
Start Converting Timestamps
Use the tool above to convert between Unix timestamps and human-readable dates. The live clock shows the current time, and you can convert any timestamp or date with timezone support—all processed instantly in your browser.