Epoch Time Converter

Introduction:

Unix time is a running count of seconds from 1 January 1970 at midnight in Coordinated Universal Time. This converter keeps that abstract number aligned with zone-aware calendars so the same instant reads correctly across daylight-saving shifts and regional rules.

Enter seconds or milliseconds to unlock ISO 8601 and RFC 2822 strings, Julian and Modified Julian day numbers, microsecond and nanosecond totals, ISO week designations, day-of-year, quarter, and a relative distance from now. You can also start with a calendar reading and obtain the exact epoch value in either seconds or milliseconds, then review a timeline chart that plots four checkpoints across the selected day.

Choose how the wall clock should be interpreted: stick with the device locale, force UTC, set a custom offset (±HH:MM), or search the supported IANA registry. The zone badge updates with the actual offset at the selected moment so you can double-check ambiguous daylight-saving transitions.

Capture the live epoch, copy any result with one click, and export CSV or DOCX snapshots to drop into API tests, incident timelines, or audit logs.

Technical Details:

Unix time measures elapsed duration since a fixed origin and records it as milliseconds or seconds from 1 January 1970 00:00:00 (Coordinated Universal Time). The tool resolves each instant into multiple representations: UTC ISO 8601 and RFC 2822 strings, a zone-adjusted ISO string, Julian and Modified Julian day numbers, microsecond and nanosecond totals, ISO week labels, day-of-year, quarter, and a natural-language relative offset.

Milliseconds are rounded down to whole seconds for the canonical epoch figure. BigInt arithmetic scales those milliseconds to microseconds and nanoseconds without precision loss. Julian quantities follow the standard tms / 86400000 relationship, ISO week numbers apply the ISO 8601 “Thursday” rule, day-of-year counts begin at one, and quarters divide the UTC calendar into four equal spans. A four-point timeline chart renders with Apache ECharts, with PNG, WebP, JPEG, and CSV exports driven by the shared chart helpers.

Calendar input obeys the preset you choose: Local defers to the device’s current zone, UTC calls Date.UTC, custom offsets parse ±HH:MM and adjust the computed milliseconds, and named IANA zones rely on Intl.DateTimeFormat to obtain the correct offset at the exact instant (including daylight-saving switches). The same formatter builds the zone-aware ISO string shown beside the preset badge.

Zoned date input → epoch (procedure)

1. Parse year, month, day, hour, minute from the input field.
2. If Local, interpret using the device’s current time zone.
3. If UTC, convert with Date.UTC(Y,M,D,h,m).
4. If Offset, parse ±HH:MM and subtract that offset from UTC.
5. Otherwise, use the named IANA zone to compute its offset at that moment.
6. Return milliseconds since the epoch and the standardized outputs.

Units, precision & rounding

• Seconds are rounded down from milliseconds using the floor function; microseconds and nanoseconds multiply the truncated millisecond count.
• Julian Day and Modified Julian Day display with five decimals.
• ISO 8601 and RFC 2822 outputs render in UTC, while the zone-aware ISO string appends the actual offset at the selected instant.
• ISO week numbers follow ISO 8601 and are padded to two digits; day-of-year runs 1–366; quarters enumerate Q1–Q4.
• “Relative” descriptions use whole units (y, d, h, m, s) based on magnitude.

Networking & storage

Processing occurs in the browser with no network requests; nothing is transmitted or stored on a server.

Performance & determinism

Conversions are constant‑time and stateless. Identical inputs and zone choices yield identical outputs; the “Locale” view depends on device settings, and the “Relative” line depends on the current moment.

Assumptions & limitations

• Heads‑up Minute‑only datetime input; seconds are not captured on input.
• Epoch seconds are truncated toward negative infinity via floor.
• Daylight saving transitions can produce repeated or skipped local times.
• Zone badges display the offset for the selected instant; ambiguous fall transitions show the earlier offset.
• Julian Day and Modified Julian Day are displayed to five decimals.
• IANA zone availability depends on the runtime environment.
• Locale date/time strings vary by user settings and language.
• Invalid offset patterns are treated as zero offset.
• Very large or extreme dates may exceed the host Date range.
• Relative wording rounds to whole units and is approximate.
• Microsecond and nanosecond totals require BigInt support; legacy runtimes leave the fields blank.

Edge cases & error sources

• Empty datetime input performs no conversion until a value exists.
• Non‑numeric epoch input coerces to zero.
• Negative epochs floor to the next more negative integer second.
• Offsets like +2 or +0200 are rejected and treated as +00:00.
• Ambiguous times at fall transition resolve to the zone’s offset at that minute.
• Non‑existent spring transition times map to the next valid instant.
• Unsupported IANA names fall back to the provided set only where available.
• Locale rendering can swap day/month order and clock style by region.
• Copying values reflects the current tab and any filters you applied.
• Rounding differences appear when comparing JD/MJD to higher precision sources.
• System clock drift affects the “Live” and “Relative” displays.
• Trailing spaces in filters yield no matches until removed.

Scientific & standards context

Outputs align with ISO 8601 date/time notation, RFC 2822 date syntax, IANA time zone identifiers, and standard Julian Day conventions.

Privacy & compliance

No data is transmitted or stored server‑side. Results reflect user input and device capabilities only.

Step‑by‑Step Guide:

Epoch time and calendar date conversions with zone‑aware interpretation:

1. Choose your starting point: Epoch or Datetime.
2. For epoch, enter a number and pick seconds or milliseconds.
3. For datetime, type a date and time, then select a zone or offset.
4. Use Local, UTC, Offset, or an IANA zone.
5. Review ISO, RFC, JD/MJD, and parts; copy or download if needed.
6. Optionally filter zones to compare local readings across regions.

Example. Enter 0 seconds and select UTC to see the epoch origin with JD 2440587.5 and MJD 40587.0.

You now have a precise instant you can reference, share, or compare across locations.

FAQ:

Troubleshooting:

• Nothing updates after typing: ensure a valid number or a complete date and time.
• Wrong local time: verify the selected zone or offset matches your intent.
• Unexpected day order: the “Locale” view follows your device’s region settings.
• Offset rejected: use ±HH:MM with leading zeros, for example +05:30.
• Duplicate or missing hour: you are crossing a daylight saving change; switch to UTC to verify.
• No zones listed: your environment may not expose the full IANA list; try UTC or Offset.

Advanced Tips:

• Tip Capture a reference instant, then compare zone outputs under the Zones tab.
• Tip Use a custom offset to model systems that log with fixed offsets.
• Tip Prefer ISO 8601 when sharing times in documents or filenames.
• Tip Compare JD/MJD values to confirm two timestamps refer to the same instant.
• Tip Use UTC for audits, then add local views for human‑friendly context.
• Tip Keep unit selection visible when alternating between epoch and datetime inputs.

Glossary:

Unix time

Elapsed seconds since 1 January 1970 00:00:00.

Epoch seconds

Epoch value truncated to whole seconds.

Epoch milliseconds

Epoch value at millisecond resolution.

ISO 8601

Standardized date and time text format.

RFC 2822

Internet message date string style.

Julian Day (JD)

Continuous day count used in astronomy.

Modified Julian Day (MJD)

Julian Day minus 2400000.5.

IANA time zone

Named region defining civil time rules.

Offset

Difference from UTC written as ±HH:MM.

Daylight saving

Seasonal clock change affecting local time.