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Unix Timestamp Basics
A Unix timestamp represents the number of seconds that have elapsed since January 1, 1970 00:00:00 UTC, commonly known as the Unix epoch. This epoch was chosen as a convenient round number to mark the start of the Unix era. Before this date, timestamps are represented as negative numbers, while dates after the epoch use positive values.
The Unix timestamp system was developed in the early 1970s as part of the Unix operating system design. Its simplicity—storing time as a single integer—made it efficient for computing and comparing dates. Unlike date strings that require parsing, timestamps can be compared mathematically with ease. This universal format became the standard for APIs, databases, and programming languages worldwide.
Timestamp Formats Explained
Timestamps come in two primary formats: seconds and milliseconds. JavaScript's Date.now() returns milliseconds (13 digits like 1747488000000), while Python's time.time() and Go's time.Now().Unix() return seconds (10 digits like 1747488000). Most Unix systems and APIs use seconds by default, while languages designed for web development typically use milliseconds.
Date.now() → 1747488000000
time.time() → 1747488000
When converting between formats, multiply or divide by 1000 accordingly. Most modern APIs accept both formats, but always verify the documentation for your specific use case.
Frequently Asked Questions
What is the Unix epoch?
The Unix epoch is January 1, 1970 00:00:00 UTC. All Unix timestamps are measured as seconds elapsed from this point.Why do some timestamps have 13 digits?
Timestamps with 13 digits are in milliseconds (like JavaScript uses). Those with 10 digits are in seconds (like Python uses). Multiply milliseconds by 1000 to convert to seconds.Can timestamps represent dates before 1970?
Yes, negative timestamps represent dates before the Unix epoch. For example, -86400 represents December 31, 1969.What happens in 2038?
Older 32-bit systems cannot represent timestamps beyond January 19, 2038 03:14:07 UTC. Modern systems use 64-bit integers, avoiding this limitation.How do I handle timezones?
Unix timestamps are always in UTC. When displaying to users, convert to their local timezone using JavaScript'stoLocaleString() or similar methods.