BYTETOOLS

Date Format Converter

Convert any date between ISO 8601, US, European, RFC 2822 and custom token formats. Includes a bulk mode that reformats a whole pasted list at once.

What is the Date Format Converter?

The ByteTools Date Format Converter takes a date written in one style and rewrites it in another. Paste 03/04/2025 and tell the tool whether that is March 4th or April 3rd, and you instantly get the ISO 8601, US, European, RFC 2822, RFC 3339 and Unix-timestamp versions of the same day, plus a long written form.

  • Explicit day-first / month-first control — no silent guessing
  • ISO 8601, US, European, RFC 2822, RFC 3339 and Unix output
  • Custom pattern builder with YYYY, MMM, DD, HH, mm tokens
  • Bulk mode converts a pasted list line by line
  • Copy or download the converted output
  • Runs entirely offline in your browser

How to use the Date Format Converter

  1. 1

    Choose whether your input is day-first, month-first or ISO order.

  2. 2

    Type or paste the date into the input box.

  3. 3

    Read the converted date in every standard format at once.

  4. 4

    Optionally enter a custom pattern such as DD MMM YYYY to build your own format.

  5. 5

    Switch to bulk mode to paste a whole list and copy or download the converted column.

About the Date Format Converter

The ByteTools Date Format Converter takes a date written in one style and rewrites it in another. Paste 03/04/2025 and tell the tool whether that is March 4th or April 3rd, and you instantly get the ISO 8601, US, European, RFC 2822, RFC 3339 and Unix-timestamp versions of the same day, plus a long written form.

It exists because date strings are the most common source of silent data bugs. Spreadsheets, log files, CSV exports and APIs all disagree about whether the day or the month comes first, and a wrong guess quietly shifts records by months. Here you state the input order explicitly, so nothing is guessed for you.

There is also a custom pattern box using familiar YYYY / MM / DD tokens, and a bulk mode that converts an entire pasted column line by line. Everything runs in your browser with JavaScript — your dates are never uploaded to a server, so it is safe for customer records and internal exports.

Frequently asked questions

What is the ISO 8601 date format?

ISO 8601 writes dates as YYYY-MM-DD, so 4 March 2025 becomes 2025-03-04. Because the fields run from largest to smallest, ISO dates sort correctly as plain text and are unambiguous in every country, which is why databases and APIs prefer them.

How do I know if 03/04/2025 is March 4 or April 3?

You cannot tell from the string alone — that is exactly the ambiguity this tool removes. Pick day-first if the data came from Europe, Australia or most of Asia, and month-first if it came from a US source, then check the long written output to confirm you chose correctly.

Can I convert a whole column of dates at once?

Yes. Turn on bulk mode and paste one date per line. Every line is converted using the same input order and output format, and lines that cannot be parsed are flagged rather than silently dropped so you can fix them.

What is the difference between RFC 2822 and RFC 3339?

RFC 2822 is the human-readable email header style, like Tue, 04 Mar 2025 00:00:00 +0000. RFC 3339 is a stricter profile of ISO 8601 used in APIs and JSON, like 2025-03-04T00:00:00Z. Both describe the same instant in different clothes.

Which time zone are the converted dates in?

Dates are treated as local calendar days and rendered as-is. The Unix timestamp and UTC outputs show the instant of that local date and time in UTC, so they can differ by a few hours from the calendar date if you are far from Greenwich.

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