What Is a Unix Timestamp?
A Unix timestamp represents an instant relative to January 1, 1970, 00:00:00 UTC, the Unix Epoch. Seconds are the conventional POSIX unit; many APIs and languages also use milliseconds, microseconds, or nanoseconds for additional precision. Negative values represent instants before the epoch.
The numeric timestamp does not contain a timezone. UTC, browser-local time, and an offset-based display can therefore describe the same instant differently without changing the underlying timestamp.
Seconds, Milliseconds, Microseconds, and Nanoseconds
Current timestamps are often 10 digits in seconds, 13 in milliseconds, 16 in microseconds, or 19 in nanoseconds. Auto-detection follows those common lengths. Historical, negative, short, or far-future values can be ambiguous, so select the input unit explicitly when you know it.
Numeric conversions preserve fractional precision through nanoseconds. Calendar output uses JavaScript's Date model, which stores milliseconds, so smaller fractions do not change the displayed date and time.
UTC, Local Time, Timezones, and DST
Timestamp-to-date conversion is unambiguous: the number identifies an instant, and the tool shows that instant in UTC and in your browser's timezone. Date-to-timestamp conversion requires an interpretation. Choose Browser Local for a wall-clock time in your current timezone, or UTC when the entered fields already describe UTC.
Daylight-saving transitions can skip a local time or repeat it with two different offsets. The tool rejects skipped local times. For an ambiguous repeated time, use a timezone-aware converter or an explicitly offset timestamp when the exact occurrence matters.
Leap Seconds and the Year 2038 Boundary
POSIX time treats every day as if it contained exactly 86,400 seconds and does not apply UTC leap seconds. It is therefore designed for consistent civil timestamp conversion, not astronomical elapsed-time measurement across leap-second events.
The signed 32-bit maximum, 2147483647, corresponds to January 19, 2038 at 03:14:07 UTC. Modern 64-bit time representations avoid that specific overflow boundary, although every runtime and date library still has its own supported range.
Common Timestamp Formats Explained
Unix seconds
1781006400Whole or fractional seconds relative to the Unix Epoch.
Unix milliseconds
1781006400000Milliseconds relative to the epoch; this is the unit returned by JavaScript Date.now().
RFC 3339 / ISO-style
2026-06-09T12:00:00ZA date-time string with an explicit UTC marker or numeric offset, commonly used by APIs.
HTTP-date
Tue, 09 Jun 2026 12:00:00 GMTThe fixed UTC date form generated for HTTP header fields.
Continue Your Developer Workflow
Inspect iat, nbf, and exp claims with the JWT Decoder & Debugger, format API payloads using the JSON Formatter & Validator, build recurring schedules with the Cron Expression Builder, or compare regional wall-clock times in the Time Zone Converter & Meeting Planner.
Timestamp Standards and References
POSIX defines the interpretation of seconds since the Epoch. Internet date-time strings are profiled by RFC 3339, while the HTTP-date grammar appears in RFC 9110. JavaScript's millisecond timestamp behavior is documented by MDN Date.now(). External references open in a new tab.
Private Browser-Based Conversion
Timestamp parsing, date conversion, difference calculations, code examples, and recent-history storage run in your browser. The tool does not send entered timestamps to a conversion server. Recent conversions are stored only in this browser's local storage and can be cleared from the page.