MM/DD or DD/MM? How Countries Write Dates, and the ISO Fix

Computed from CLDR 48 locale data, 01/02/2027 means Jan. 2, 2027 in U.S. English and Feb. 1, 2027 in the United Kingdom (UK), because month/day (MM/DD) and day/month (DD/MM) orders look the same on the page. CLDR is the Common Locale Data Repository published by the Unicode Consortium; operating systems and browsers draw on locale data like it. We computed the short date for Jan. 2, 2027 in 27 locales and grouped them by order below. The fix, the International Organization for Standardization (ISO) date 2027-01-02, follows the tables, and a one-page reference card to print is at the end.

How do 27 locales write Jan. 2, 2027?

We formatted Jan. 2, 2027 with CLDR 48 data through International Components for Unicode (ICU) 78.3, using the short date style of the JavaScript Intl.DateTimeFormat application programming interface (API) in Node.js, and again with a two-digit month, two-digit day and four-digit year. These are locale defaults, not laws. A country’s people and agencies may also use other forms, and the result depends on the locale, not on the country alone.

Month first (MM/DD/YYYY)

Locale	Short style	Two-digit style
United States (en-US)	1/2/27	01/02/2027
Philippines (en-PH)	1/2/27	01/02/2027

Day first (DD/MM/YYYY)

Locale	Short style	Two-digit style
United Kingdom (en-GB)	02/01/2027	02/01/2027
Australia (en-AU)	2/1/27	02/01/2027
India (en-IN)	02/01/27	02/01/2027
New Zealand (en-NZ)	02/01/2027	02/01/2027
Ireland (en-IE)	02/01/2027	02/01/2027
Germany (de-DE)	02.01.27	02.01.2027
Switzerland (de-CH)	02.01.27	02.01.2027
France (fr-FR)	02/01/2027	02/01/2027
Italy (it-IT)	02/01/27	02/01/2027
Spain (es-ES)	2/1/27	02/01/2027
Mexico (es-MX)	02/01/27	02/01/2027
Brazil (pt-BR)	02/01/2027	02/01/2027
Netherlands (nl-NL)	02-01-2027	02-01-2027
Poland (pl-PL)	2.01.2027	02.01.2027
Russia (ru-RU)	02.01.2027	02.01.2027
Turkey (tr-TR)	2.01.2027	02.01.2027

Year first (YYYY-MM-DD)

Locale	Short style	Two-digit style
Canada, English (en-CA)	2027-01-02	2027-01-02
Canada, French (fr-CA)	2027-01-02	2027-01-02
Sweden (sv-SE)	2027-01-02	2027-01-02
Lithuania (lt-LT)	2027-01-02	2027-01-02
South Africa (en-ZA)	2027/01/02	2027/01/02
Japan (ja-JP)	2027/01/02	2027/01/02
China (zh-CN)	2027/1/2	2027/01/02
South Korea (ko-KR)	27. 1. 2.	2027. 01. 02.
Hungary (hu-HU)	2027. 01. 02.	2027. 01. 02.

Of the 27 locales, 2 put the month first, 16 put the day first and 9 put the year first. Short styles that drop the leading zero, such as 2/1/27 in Spain and Australia, read the same way as the two-digit forms; the order is what matters. Canada appears only as the CLDR defaults for Canadian English and French. We did not confirm any Canadian government rule for date format, so this story does not state one.

Some locales default to another calendar altogether. In our run, the Persian locale fa-IR showed the Solar Hijri date 1405/10/12 for Jan. 2, 2027, so a date can differ by calendar as well as by order.

Which dates read two ways in 2027?

Any day number from 13 to 31 can only be a day, so a date such as 13/01/2027 has one reading. A date is ambiguous when both numbers are 12 or lower and they differ. By our computation, there are 144 pairs from 01/01 to 12/12, and every one is a real date in 2027. Of those, 132 read two ways. The other 12, from 01/01 to 12/12 with matching numbers, read the same either way.

Written as	Month first reads	Day first reads
01/02/2027	Jan. 2, 2027	Feb. 1, 2027
03/04/2027	Mar. 4, 2027	Apr. 3, 2027
05/06/2027	May 6, 2027	June 5, 2027
07/08/2027	July 8, 2027	Aug. 7, 2027
11/12/2027	Nov. 12, 2027	Dec. 11, 2027
03/03/2027	Mar. 3, 2027	Mar. 3, 2027 (same)

The same slash-style trap shows up in what ISO 8601 is, where 05/01/2026 is May 1 or Jan. 5 depending on the reader.

What is the ISO fix for MM/DD versus DD/MM?

ISO’s help center describes the date as “YYYY-MM-DD (year-month-day)” and gives the example “2022-09-06” for Sept. 6, 2022 (July 31, 2025). Under that rule, Jan. 2, 2027 is 2027-01-02. A four-digit number in first place can only be the year, so the text has one reading whatever the reader’s habit. Several locales in our table already default to year-first forms, including Canadian English and French, Sweden, Lithuania and Hungary.

The wider format, including times and the Z suffix, is in our ISO 8601 guide. Week dates such as 2026-W53-5 for Jan. 1, 2027 are in ISO week numbers explained.

What do U.S. and U.K. government style guides say?

Two style guides settle the written-out form, not the all-numeric one.

Guide	What it says
U.S. Government Publishing Office (GPO) Style Manual 2016, rule 12.9c	Examples: “June 29, 1985 (not June 29th, 1985)” and “June 1985 (not June, 1985)”
GOV.UK A to Z style guide	“Do not use ordinal numbers for the day”, as in “2 June and not 2nd June”; “do not use a comma between the month and year”, as in “4 June 2017”

The GPO manual gives no rule for all-numeric order, so we do not claim it requires MM/DD. We also did not confirm style rules from other governments, such as those of Canada, Australia or the European Union, because the pages were not reachable for us.

How do you write a date so nobody misreads it?

1. Spell out the month when space allows: Jan. 2, 2027 in U.S. style or 2 January 2027 in the day-first style that GOV.UK uses.
2. In tables, filenames and data that cross borders, use 2027-01-02.
3. Treat any slash date with both numbers at 12 or lower as ambiguous, and add the month name.
4. Keep the year at four digits, since 1/2/27 adds a second question about the century.

For planning, our January printable calendar and printable yearly calendar show every date with its month name.

Date formats reference card to print

The free one-page card lists the 27 locales by order, adds the ISO rule and leaves five blank rows for the dates you write most often, with room for the month-first, day-first and ISO forms. It follows the table above and carries the CLDR 48 and ISO sources.