Unix timestamp converter
Convert Unix seconds or milliseconds to UTC dates, and back.
UTC only: YYYY-MM-DDTHH:mm:ss.SSSZ. Seconds and milliseconds are optional.
Enter a timestamp or UTC date to convert.
Years 0001–9999. UTC only. Precision: 1 millisecond; leap seconds are not supported.
Related tools
A timestamp from a log or an API is easier to understand as a calendar date. Paste the number, explicitly choose seconds or milliseconds, and read its UTC equivalent. For the reverse calculation, enter a UTC date and time to get both numeric forms. This tool avoids guessing units from the number of digits. It runs locally without saving your input, and the Now button captures a single instant from your device clock rather than starting a ticking display.
How to use
- Choose timestamp to date or date to timestamp.
- For a number, select seconds or milliseconds before interpreting the result.
- For a date, enter the shown year-month-day format and a UTC time.
- Use Now or the example if needed, then copy the three result lines.
What it handles
- Accepts negative timestamps for dates before the Unix epoch.
- Seconds support up to three decimal places with a dot or comma; milliseconds must be integers.
- Supports years 0001–9999 with calendar validation, including leap years.
- Always displays UTC ISO format, seconds and milliseconds together.
- No automatic unit guessing, local-time interpretation or input storage.
FAQ
What is the difference between seconds and milliseconds?
One second contains 1,000 milliseconds. Unix timestamps are commonly expressed in seconds, while JavaScript dates use milliseconds. Choose the unit used by your source system. A wrong selection can produce a completely different date even when the number itself is valid.
Which time zone does the date field use?
The date field always means UTC, regardless of your device’s time zone. The output ends in Z to make that explicit. Convert a local appointment to UTC with a time-zone converter first; this field does not resolve regional daylight-saving gaps or repeated hours.
Can I convert dates before 1970 or fractional seconds?
Yes. Negative values refer to instants before 1970-01-01 at midnight UTC. For example, −0.001 seconds is one millisecond before that point. Use a standard minus sign when typing. This tool supports millisecond precision, not microseconds, nanoseconds or leap-second notation.
Why is my date or timestamp rejected?
Dates must be real calendar values between years 0001 and 9999. February 30, a time of 24:00 and leap seconds are rejected. Use digits without grouping or exponent notation. Numeric milliseconds must be whole numbers; seconds can have up to three decimal places.
Updated