Date Format Converter (DD/MM/YYYY ↔ MM/DD/YYYY ↔ ISO 8601)

About the Date Format Converter (DD/MM/YYYY ↔ MM/DD/YYYY ↔ ISO 8601)

Paste one date or a whole list — 04/03/2026, March 4, 2026, 4. März 2026, 2026-03-04, 20260304, 2026-W10-3 — and get each one back in the format you need: ISO 8601 (2026-03-04), day-month-year (04/03/2026), month-day-year (03/04/2026), year-month-day, an ISO week or ordinal date, or a short, medium, long or full date in any of dozens of languages, written by your browser’s copy of the Unicode CLDR data.

A date such as 03/04/2026 could be 3 April or 4 March. The converter reads it the way the other dates in your list settle it (a 13/04/2026 elsewhere means day first), otherwise the way your country writes dates, and marks every such date with the other reading. A reference shows how dates are written in any country: the order and separators, the clock, the first day of the week and the calendar its language uses by default. Nothing leaves your browser.

Common uses

• Turning dates from a US system into ISO 8601 or day-first dates for a spreadsheet, and back.
• Checking a list of dates for ones that could be read two ways before importing it.
• Writing a date the way a client or a form in another country expects.
• Finding the ISO week date or day of the year of a list of dates.

Ambiguous dates: day first or month first?

Numbers alone do not say which part is the day: 03/04/2026 is 3 April in most of the world and 4 March in the United States. The converter settles it in this order: a part over 12 is a day; then other dates in the same list (if any can only be day first, the ambiguous ones are read day first too); then the usual order of the country chosen in the converter, which starts as the one at the top of the page. Every date that could be read another way is flagged with the other reading, and Ambiguous dates lets you choose the order yourself. Dates with a month name, ISO 8601 dates and dates whose day is over 12 are never ambiguous.

ISO 8601 forms

ISO 8601 writes the year, the month and the day from largest to smallest: 2026-03-04. It also has a week date — the ISO week-numbering year, W, the week number 01–53 and the weekday 1–7 starting on Monday (2026-W10-3) — and an ordinal date: the year and the day of the year, 001 to 366 (2026-063). The basic form leaves out the hyphens (20260304). The converter reads and writes all of them; their grammar is collected in RFC 3339, the internet profile of ISO 8601, whose full date is YYYY-MM-DD.

Two-digit years

A year like 26 is read within the 80 years before and 19 after the current year — the rule of ICU, the library behind most browsers’ date formats (ICU SimpleDateFormat: “within 80 years before and 20 years after” the moment the format is created). So in a year when that window runs from 1946 to 2045, 45 is 2045 and 46 is 1946. For birth dates or old records choose 19xx, for future dates 20xx. Every date with a two-digit year is marked in the results.

How countries write dates

The reference shows, for any country, what your browser’s Unicode CLDR data gives: the numeric date in English as written there and in the country’s main language (only where the browser has that data: Chrome has no English for Brazil, for example, and would write US English, so Brazil shows Portuguese alone), with its order and separator, the short, medium, long and full forms, a time of day, the usual 12- or 24-hour clock and the first day of the week (CLDR timeData and weekData). Some languages use another calendar by default — Thai the Buddhist era (2026 is 2569), Persian the Solar Hijri calendar — and some use their own digits; the reference names both. Browsers update their CLDR data from time to time, so these defaults can change: Arabic for Saudi Arabia, for example, used the Umm al-Qura calendar by default in older CLDR versions and the Gregorian calendar in newer ones.

Limitations

• One date per line, up to 10,000 lines. Dates with a month name are read in English and 16 other languages.
• Dates are calendar dates: times are kept as written, never converted between time zones (use the Timezone Converter for that).
• Unix timestamps and spreadsheet serial numbers are not read: use the Timestamp Converter for timestamps.
• Language formats come from your browser’s CLDR data, so two browsers can write a date slightly differently (a comma, a dot after the day).

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.