Date & Time

Date Format Converter

Reformats a list of dates into one consistent form, and flags the ones that were ambiguous.

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Processing happens locally in your browser. What you paste or load is processed by this page and is not uploaded to a server. Nothing is stored unless you use a control that says it stores something, and you can clear anything this site has kept from the privacy page.

How to use this tool

  1. Paste the dates, one per line, mixed formats and all.
  2. Choose the output format you want them all in.
  3. Set how slash dates should be read if you know the source convention. Leave it on guess only if you are prepared to check the flags.
  4. Select Reformat and read the third column, which says how each line was interpreted.

What date format converter does

Cleaning a column of dates that arrived in three different formats is a common and genuinely risky job. 03/04/2026 is the third of April to most of the world and the fourth of March in the United States, and there is nothing in the value itself to tell you which. This page flags every line where both numbers are twelve or under, and lets you set the input order rather than accepting a guess.

The output side offers the formats people actually need: ISO 8601 for anything a machine will read, day-first and month-first slash forms for the two local conventions, spelled-out long forms for documents, compact YYYYMMDD for filenames and partition keys, and an SQL timestamp. The third column reports how each line was read, so the conversion is auditable rather than magic.

Frequently asked questions

It flags it. Both numbers are twelve or under, so the value is genuinely ambiguous and no tool can resolve it from the value alone. The default assumption is day-first and the row says so; if you know the source convention, set it and the flag goes away.

Exactly which interpretation produced each output — day-first, month-first, year-first, epoch, or a browser fallback. It makes the conversion auditable, which is what you want before running a cleaned column back into a system.

The compact YYYYMMDD form, or the ISO date. Both sort correctly as text, which slash formats do not — a directory of files named 01-03-2026 sorts by day of the month across every year, which is almost never what anyone wanted.

Yes, in both orders — "4 Mar 2026" and "March 4, 2026" — with full or three-letter month names. Those forms are unambiguous, which is why they are worth using in anything a human will type.