Unix timestamp converter

Unix time counts from one UTC instant

A Unix timestamp represents elapsed time since 1970-01-01 00:00:00 UTC, excluding leap-second representation used by some specialized systems. Many APIs use whole seconds, while browser and JavaScript timestamps commonly use milliseconds.

Seconds and milliseconds differ by 1,000

The same instant is `1767225600` seconds or `1767225600000` milliseconds. Selecting the wrong unit can produce a date near 1970, a date far in the future, or a value outside the browser’s supported date range.

ISO input should include a timezone

Use `Z` for UTC or an explicit numeric offset such as `-06:00`. An ISO-like date without a timezone may be interpreted in the browser’s local timezone, which makes results device-dependent. This tool rejects date-to-timestamp input without an explicit `Z` or offset.

Local display is informational

The UTC ISO result identifies the instant consistently. The local result uses the current browser’s timezone and locale settings. Daylight-saving rules and historical timezone data come from the browser environment and can vary by platform version.

Round-trip a value before storing it

Convert the source timestamp to UTC ISO, then convert that ISO value back with the same seconds-or-milliseconds selection. The integer should return unchanged unless the source included subsecond precision that the chosen unit cannot represent. Save the unit beside the field name—such as `created_at_seconds`—instead of relying on the number’s length. For distributed logs, retain UTC for ordering and add local formatting only for display. A timestamp proves neither when an event was received nor whether a device clock was accurate; record server receipt time separately when that distinction matters.

This converter does not model leap seconds, non-Gregorian calendars, server-specific date limits, or every historical timezone rule. Verify unit, timezone, API format, and database range before storing or comparing timestamps.