Timestamp Converter
Convert signed Unix seconds or milliseconds and strict ISO dates
Choose Unix seconds or milliseconds explicitly. Dates use strict ISO syntax; date-times without an offset use the browser timezone.
Browser timezone: UTC · Date-only means midnight UTC. Invalid dates and local clock gaps/folds are rejected.
The full guide also includes pitfalls, worked examples, snippets, FAQs, and related tools for checking results or troubleshooting.
About this tool
Convert a signed Unix value using an explicit seconds or milliseconds setting. Seconds allow up to three decimal places; milliseconds must be integers. Date input accepts strict Gregorian YYYY-MM-DD or YYYY-MM-DDTHH:mm[:ss[.SSS]], with optional Z or ±HH:mm on date-times. Date-only values mean midnight UTC; date-times without an offset use the displayed browser timezone. Invalid calendar dates and missing or repeated local times at clock changes are rejected. The local date picker follows the same timezone rule. Results include UTC, ISO, browser-local time, relative time at conversion, and Unix values. Quick offsets add fixed elapsed durations and preserve milliseconds: 30 days is not a calendar month. ISO calendar input supports years 0001–9999; numeric input is limited to the JavaScript Date range. Processing is local and input is not saved by this tool.
Failure Clinic (Common Pitfalls)
A numeric unit changes the instant
Cause: Seconds and milliseconds differ by a factor of 1,000; digit length is not a universal unit guarantee.
Fix: Use the unit specified by the source API or log format.
Relative time is a snapshot
Cause: The result is calculated when converted; it does not prove that a token is valid or an event really occurred.
Fix: Reconvert for a fresh relative value and validate application rules in the owning system.
Scenario Recipes
Check a millisecond log value
Goal: Keep a subsecond remainder while moving an event one hour.
- Choose Milliseconds and enter 1700000000123.
- Convert and verify ISO 2023-11-14T22:13:20.123Z.
- Click +1 hour and verify 2023-11-14T23:13:20.123Z.
Result: Unix milliseconds become 1700003600123; the .123 remainder stays intact.
Distinguish a repeated local time
Goal: Identify the intended New York instant at a fall clock rollback.
- Enter 2026-11-01T01:30:00-04:00 and convert.
- Compare it with 2026-11-01T01:30:00-05:00.
Result: UTC changes from 05:30Z to 06:30Z although the local clock text is the same.
Production Snippets
Worked example
text
seconds -1 → 1969-12-31T23:59:59.000Z
seconds 1.5 → 1970-01-01T00:00:01.500Z
2026-02-30 → rejectedSuggested Workflow
Document Handoff: Split a PDF, Check Extracted Text, and Deliver the Right Version
Prepare smaller PDF bundles, choose text extraction or OCR, check a known passage, and make the recipient’s version and access instructions clear.
Coordinate Release Times with UTC and Check the DST Boundary
Reproduce January and July 2026 conversions for New York, Shanghai, and London, then distinguish the two New York 01:30 times at the end of daylight saving time.
Frequently Asked Questions
Does it guess seconds versus milliseconds?
No. Choose the numeric unit explicitly. In seconds mode -1 is 1969-12-31T23:59:59.000Z; in milliseconds mode -1 is 1969-12-31T23:59:59.999Z.
Which date formats are accepted?
Strict YYYY-MM-DD or YYYY-MM-DDTHH:mm[:ss[.SSS]], optionally ending with Z or ±HH:mm on a date-time. Natural-language dates, February 30, 24:00 and leap-second notation are rejected.
Which timezone applies without an offset?
A date-only value uses UTC midnight. An offsetless date-time and the local picker use the displayed browser timezone. Gaps and folds are rejected; use an explicit offset to identify an instant.
Does adding one day preserve the local clock time?
Offsets add fixed elapsed time: one day is 24 hours, one week is 168 hours, and 30 days is 720 hours. Across DST, the displayed local clock can change.
Are milliseconds preserved and inputs saved?
Millisecond numeric input and up to three decimal places in seconds are preserved. Offsets keep the remainder. Inputs are processed locally and this tool does not store them.
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