Date & time

Unix Timestamp Converter

Convert Unix timestamps (seconds or milliseconds) to readable dates and back, with UTC, your local time zone, and Asia/Kathmandu support alongside ISO 8601 and relative-time output.

Free to use · Runs in your browser · No account required

Processed locally in your browser

Nothing you enter here is uploaded, transmitted to a server, or stored by this tool. Timestamps are converted locally; nothing you enter is sent anywhere.

Runs entirely in your browser — nothing is sent to a server

How to use this tool

  1. 1Pick a display time zone — UTC, your browser's local zone, or Asia/Kathmandu are common choices.
  2. 2Paste a Unix timestamp and convert it to a date, or use current time to see right now.
  3. 3The unit (seconds vs milliseconds) is auto-detected from the number of digits — override it if needed.
  4. 4Or go the other way: pick a date and time and convert it to Unix seconds and milliseconds.

Unix time, seconds vs milliseconds

Unix time counts seconds (or milliseconds, depending on the API) since 1970-01-01T00:00:00Z — the epoch. Most Unix/POSIX APIs and PostgreSQL's extract(epoch from …) use seconds; JavaScript's Date.now() and most JSON APIs from browser-side code use milliseconds. Mixing the two up is one of the most common date bugs in web backends — a millisecond value treated as seconds lands in the year 48108, and a seconds value treated as milliseconds lands in 1970.

Nepal Standard Time (Asia/Kathmandu) is UTC+05:45 — one of a handful of time zones with a 15-minute offset component, which trips up date-math that assumes whole-hour offsets.

Frequently asked questions

How does the converter know if my number is seconds or milliseconds?

It compares the magnitude of the number against typical ranges for current dates: 10-digit values are treated as seconds and 13-digit values as milliseconds. You can override the detected unit manually.

Can I convert dates before 1970?

Yes. Negative Unix timestamps representing dates before the epoch are supported, subject to your browser's Date range.

Does Asia/Kathmandu really use a 45-minute UTC offset?

Yes — Nepal Standard Time is UTC+05:45, one of the few time zones with a 15-minute offset component.

Related writing

Planned — not yet published

  • Planned
    Unix time, ISO 8601, and RFC 3339: picking the right format for an API— Interop pitfalls between JSON APIs and date libraries.
  • Planned
    Why your dates are off by 5:45 — working with Nepal Time (NPT)— The half-hour/quarter-hour UTC offsets developers forget.
  • Planned
    Storing timestamps correctly in PostgreSQL: timestamptz vs timestamp— How column choice interacts with app-level time zone bugs.

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