What is a Unix timestamp?
A Unix timestamp is the number of seconds that have elapsed since 00:00:00 UTC on Thursday, 1 January 1970 — the Unix Epoch. It is the universal standard for representing moments in time in computer systems. Unlike human date formats (which vary by locale, language, and time zone), a Unix timestamp is a single unambiguous integer that means the same thing on every computer in every country. The timestamp 1700000000, for example, represents exactly one specific moment in time regardless of whether it is interpreted in New York, Tokyo, or London.
Unix timestamps are used in operating system file metadata, database records, API responses, authentication tokens (JWT exp and iat claims), log files, cache headers (Cache-Control, Expires), and virtually every system that needs to store, compare, or transmit a point in time.
Seconds vs milliseconds
The original Unix timestamp is measured in seconds. JavaScript's Date.now() and many modern APIs return milliseconds (seconds × 1000). A 10-digit number (like 1700000000) is seconds. A 13-digit number (like 1700000000000) is milliseconds. The converter auto-detects which you have entered based on the number of digits and converts accordingly. Both are shown in the output so you can copy whichever your application needs.
UTC vs local time
Unix timestamps are inherently UTC — they count seconds from a specific UTC moment. When displaying a timestamp as a human-readable date, you must decide whether to show it in UTC or in a local time zone. The converter shows both: the UTC representation (always unambiguous) and the local time in your browser's time zone. For server logs, database records, and API timestamps, UTC is almost always the correct choice. For user-facing display, local time is usually preferred.
Converting a date to a timestamp
The right panel converts a date and time you enter into a Unix timestamp. Enter a date and time using the date picker, and the converter shows the corresponding Unix timestamp in seconds and milliseconds. This is useful for: constructing test data with specific dates, setting expiry times in authentication tokens, calculating the timestamp for a future deployment or event, and building SQL queries with timestamp comparisons.
The Year 2038 problem
Systems that store Unix timestamps as 32-bit signed integers can represent dates only up to 03:14:07 UTC on 19 January 2038, when the value overflows. The maximum 32-bit signed integer is 2,147,483,647 — this timestamp is shown in the reference table. Modern systems use 64-bit timestamps which will not overflow for billions of years, but legacy systems and some embedded devices may still be affected. The converter uses JavaScript's 64-bit floating point numbers and handles dates well beyond 2038.