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Unix Timestamp Calculator

Unix Timestamp Calculator

Convert between Unix timestamps and readable UTC/local date-time values in seconds or milliseconds, with negative timestamp support where the browser supports it. Browse more tools in our Date & Time Calculators collection.

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Fields start empty so you can calculate your own date or time scenario. Review the inputs before relying on the result.

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What is a Unix timestamp?

A Unix timestamp represents a time relative to the Unix Epoch, 1970-01-01 00:00:00 UTC. Seconds are the common POSIX-style unit, while JavaScript Date values use milliseconds internally.

What is the difference between seconds and milliseconds?

A millisecond timestamp is 1,000 times the corresponding seconds value. Choosing the wrong unit can make a date appear thousands of years away or outside the supported range.

What does UTC mean in this calculator?

UTC output describes the same instant without a local time-zone offset. Local output formats that instant using your browser/device time zone.

Can Unix timestamps be negative?

Many modern systems and JavaScript can represent dates before the Epoch with negative values, but some external systems impose narrower ranges.

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Frequently asked questions

It represents 1970-01-01 00:00:00 UTC.
Traditionally they are expressed in seconds, but many programming environments and APIs use milliseconds.
Yes. Choose milliseconds when converting a numeric timestamp.
Yes. Timestamp-to-date mode shows both.
Yes. Date-to-timestamp mode can interpret the entered value as device local time or as UTC.
POSIX-style seconds since the Epoch treat each day as exactly 86,400 seconds and do not model leap seconds as extra timestamp seconds.
Yes where the browser Date range supports the corresponding pre-1970 instant.
No. Conversion runs in the browser.

Sources and methodology

This calculator uses transparent browser-side date/time arithmetic. The references below provide standards or official context relevant to the calculation.

The Open Group — Seconds Since the EpochPOSIX definition and calculation model for seconds since the Unix Epoch.ISO — ISO 8601 date and time formatInternational standard context for unambiguous Gregorian dates, times, UTC and intervals.
Date and time scope: Calendar, time-zone, holiday and scheduling conventions can differ by jurisdiction or organization. Check authoritative rules when a deadline, legal right, payroll event or travel schedule depends on the exact result.
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