What This Tool Does
What is a Unix Timestamp Calculator? It converts a Unix timestamp in seconds or milliseconds to a date and time, or converts a date and time to a Unix timestamp. The result includes UTC and local values plus intermediate calculation details.
Choose Timestamp → Date to enter a numeric timestamp, its Unit, and the zone used to display the local result. Choose Date → Timestamp to enter a Date, Time (24-hour), and the zone in which that clock reading should be interpreted.
How the Conversion Works
The calculator uses the Unix epoch, 1970-01-01T00:00:00Z, as its reference.
- Timestamp → Date: it adds seconds or milliseconds to the epoch, then formats that instant in the selected zone.
- Date → Timestamp: it resolves the entered wall-clock time in the selected zone, subtracts the epoch, and calculates the timestamp.
For Date → Timestamp, the input is limited to whole seconds. The displayed seconds and milliseconds are rounded with Math.round(). In formula form: timestamp (seconds) = Math.round((UTC instant - Unix epoch) / 1000).
Time Zones, Defaults, and Conventions
- The time-zone selectors contain zones supplied by your browser's
Intlimplementation. If zone enumeration is unavailable, a fixed fallback list is used. - Your browser-detected time zone is selected initially.
- Use current time fills the timestamp, date, time, and current zone-related inputs. It does not run Calculate.
- Unix time ignores leap seconds; each day is treated as exactly 86,400 seconds.
- A timestamp is an instant relative to UTC and has no time zone of its own. The zone selector controls display or interpretation of the entered date and time.
How to Use the Calculator
- Select Timestamp → Date or Date → Timestamp.
- Enter the required timestamp and choose Seconds since epoch or Milliseconds since epoch, or enter a Date and Time (24-hour).
- Choose the relevant time-zone selector: Show local time in or Interpreted as local time in.
- Click Calculate.
- After a result appears, use Copy result or Download result (.txt).
Validation and Edge Cases
Timestamp input must be a whole or decimal number and must produce an instant that JavaScript's Date object can represent. Invalid dates, out-of-range times, and unsupported zones show an error. Real calendar dates are checked, so a date such as February 30 is rejected.
- If the Date → Timestamp time field is blank, the calculator silently uses
00:00:00. - Date → Timestamp accepts second-level input only. Its timestamp and millisecond output are rounded with
Math.round(). - The calculator does not explicitly detect or report ambiguous or nonexistent local times during daylight-saving transitions. It uses a heuristic offset resolution, so take care with times in a transition gap or overlap.
- Available zones and zone validity depend on your browser's
Intlsupport.
Reading the Result
For Timestamp → Date, the result shows local time in the selected zone and the UTC date/time. For Date → Timestamp, it shows Unix timestamp seconds and milliseconds. The intermediate table includes the entered value, selected zone, UTC offset, UTC date/time, and epoch-based values.
Use Copy result to copy the plain-text result, or Download result (.txt) to download it as a text file.
Limitations and Privacy Scope
Calculator conversion runs in your browser using the entered values and browser time-zone data; it does not use an external time service. It does not account for leap seconds and does not provide official, legal, regulatory, or scheduling determinations. This local-calculation statement applies to the calculator conversion fields, not to every feature on the page: the page also loads analytics and includes an email subscription form that posts to /assets/subscribe.php.
Frequently Asked Questions
What is a Unix timestamp?
A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have elapsed since 1970-01-01T00:00:00 UTC, not counting leap seconds. Some systems express it in milliseconds instead of seconds; this calculator lets you choose which unit you mean.
Does a Unix timestamp include a time zone?
No. A Unix timestamp represents a single instant in time relative to UTC and has no time zone of its own. When converting a timestamp to a date, you separately choose which time zone to display the resulting local date/time in; when converting a date to a timestamp, you specify which time zone that date/time reading belongs to.
Does this calculator account for leap seconds?
No. Unix time by definition ignores leap seconds - every day is treated as exactly 86,400 seconds. This calculator follows that same standard convention, consistent with how virtually all computer systems and the JavaScript Date object handle Unix time.
Where does the time zone data come from?
All offsets and local times are computed using your web browser's built-in IANA time zone data via the JavaScript Intl API. The selector contains the zones your browser exposes, or a fixed fallback list when supported zone enumeration is unavailable. No external time service is used.
What happens if the Date → Timestamp time is blank?
A blank time is silently treated as 00:00:00. Enter a time when you need a value other than midnight.
Does Date → Timestamp support fractional seconds?
No. It accepts second-level input and rounds the resulting timestamp and milliseconds with Math.round().
How does the calculator handle daylight-saving time transitions?
It does not explicitly detect or report ambiguous or nonexistent local times during daylight-saving transitions. It uses a heuristic offset resolution, so check entered times that fall in a transition gap or overlap.
Does this tool give an official or legal time determination?
No. It performs a single deterministic calculation using your browser's time zone data for the values you enter. It is not legal, regulatory, or scheduling advice, and it does not consult or represent any government or institutional authority on time.