Date Calculator & Unix Timestamp Converter
Convert Unix timestamps to dates, create timestamps from local or UTC dates, add or subtract time, and calculate the difference between two dates. Calculations run entirely in your browser.
Loading current timestamp...
Updates once per second after the page loads.
Negative timestamps and fractional seconds are supported. Milliseconds must be whole numbers.
Use YYYY-MM-DDTHH:mm:ss. Components are parsed directly; free-form date strings are not accepted.
Days, months, and years use calendar arithmetic. Hours and minutes use exact elapsed duration.
Differences are exact elapsed durations. Total days are 24-hour periods, not calendar-day counts or calendar months.
How Unix timestamps work
Unix timestamps count elapsed time from January 1, 1970 at 00:00:00 UTC. The timestamp identifies an instant; UTC and local time are different ways to display that same instant. Negative timestamps represent supported dates before the Unix epoch.
Seconds versus milliseconds
Ten-digit timestamps commonly represent seconds, while thirteen-digit timestamps commonly represent milliseconds. Length alone is not proof: eleven- and twelve-digit values can be ambiguous. The tool always shows its detection and provides a manual unit override.
UTC and local-time interpretation
A date entered in Local mode uses your browser's timezone rules. UTC mode treats the same date and clock fields as UTC. Local times can be missing when clocks move forward or repeated when clocks move backward, so the tool displays offsets and warns when it can detect those cases.
Calendar arithmetic and elapsed time
Days, months, and years use calendar arithmetic. Month and year results clamp to a valid date, such as February 29 for January 31 plus one month in a leap year, or February 28 for February 29 plus one year in a non-leap year.
Hours and minutes use exact elapsed duration. Date differences also measure elapsed time, and total days are explicitly 24-hour periods rather than calendar-day, month, or year counts.
Privacy and limitations
All calculations happen locally in your browser. Entered dates and generated timestamps are not uploaded or stored.
Timezone rules come from the browser and operating system. Historical offsets and repeated DST times can vary by environment, so verify the displayed offset when legal, financial, or scheduling accuracy depends on one exact instant.
Frequently asked questions
What is a Unix timestamp?
A Unix timestamp represents elapsed time since January 1, 1970 at 00:00:00 UTC. It usually appears as seconds or milliseconds and identifies one instant independent of how that instant is displayed locally.
How does the calculator detect seconds versus milliseconds?
The automatic rule treats absolute values of at least 100,000,000,000 as milliseconds and smaller values as seconds. Eleven- and twelve-digit values are marked as potentially ambiguous, and you can override the detected unit.
Is a Unix timestamp in UTC or local time?
A Unix timestamp identifies an absolute instant based on UTC. Local time is a display or input interpretation, so this calculator shows UTC, ISO 8601, and browser-local output together.
How are month ends, leap years, and daylight saving time handled?
Month and year changes clamp to the last valid day, so January 31 plus one month becomes February 28 or 29. Calendar days preserve wall-clock time where possible, while hours and minutes are exact elapsed durations. Local DST gaps and repeated times may produce warnings.
Does McStumble send or store my dates?
No. Date calculations run in your browser, and McStumble does not send or store the entered dates or generated timestamps.
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