ISO 8601 (extended format)
YYYY-MM-DD, e.g. 2026-10-09
From the largest to the smallest field, so it sorts correctly as text.
Convert MM/DD/YYYY or DD/MM/YYYY dates to YYYY-MM-DD (and back)
Turn a US MM/DD/YYYY or day-first DD/MM/YYYY date into ISO 8601 YYYY-MM-DD, and back, by choosing the source format explicitly.
The date does not match the selected source format or does not exist (31 April, 29 February in a common year…). The year must have 4 digits.
Converted date
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How does this tool work?
Is 03/04/2026 the 4th of March or the 3rd of April? It depends on where it was written: the United States puts the month first (MM/DD/YYYY), the UK and most of the world put the day first (DD/MM/YYYY), and the ISO 8601 standard starts with the year (YYYY-MM-DD). This converter rewrites a date from one of these formats into another, in both directions, and checks along the way that the date really exists in the Gregorian calendar. It is the safest way to prepare a date for a spreadsheet, a database, an API or a reader in another country.
You choose the source format: the tool never guesses the order of day and month, because a date such as 03/04/2026 is valid either way. For DD/MM/YYYY and MM/DD/YYYY, day and month accept one or two digits and the separator can be a slash, a hyphen or a dot (9.10.2026 read as DD/MM/YYYY is 9 October 2026). The year must have four digits.
The date is then checked with the Gregorian rule: 31 April is rejected and 29 February is only accepted in leap years (divisible by 4, except century years not divisible by 400: 2000 yes, 1900 no).
Finally it is written in the target format with leading zeros. The “ISO 8601 UTC” option produces YYYY-MM-DDT00:00:00Z, midnight in Coordinated Universal Time, the date-time form of the RFC 3339 profile used by APIs. With ISO input, only the first ten characters (YYYY-MM-DD) are read: any time or offset after them is ignored.
How to use this tool
Type the date
Enter it as it appears in your document, for example 03/04/2026 or 2026-04-03.
Choose the source format
Select the order actually used by the person or software that produced the date.
Choose the target format
YYYY-MM-DD for a spreadsheet, database or file name; MM/DD/YYYY or DD/MM/YYYY for a human reader.
Copy the result
It appears as soon as the entry is valid; otherwise a message explains what is wrong.
The three date orders
A date always has the same three fields; only their order and separator change.
Month-day-year order
MM/DD/YYYY, e.g. 10/09/2026
Common in the United States.
Day-month-year order
DD/MM/YYYY, e.g. 09/10/2026
Used in the UK, most of Europe, Latin America, Africa and much of Asia.
UTC date-time (RFC 3339)
YYYY-MM-DDT00:00:00Z
“T” separates date and time; “Z” means a UTC offset of 00:00.
The date order used by each language and country is recorded by the Unicode CLDR project, which browsers rely on to display localized dates.
Use cases
Open a US export in a European spreadsheet
Convert 10/09/2026 (MM/DD) to 2026-10-09 so it is not read as 10 September.
Prepare a date for an API or a database
SQL DATE columns and most JSON APIs expect YYYY-MM-DD.
Write for a reader abroad
Turn an ISO date into the order your reader expects, or spell out the month to remove any doubt.
Check a suspicious date
An entry such as 02/29/2025 or 06/31/2026 is flagged as non-existent.
Examples
One entry, two different dates
This is why the source format must be chosen.
Input
03/04/2026Result
DD/MM → 2026-04-03; MM/DD → 2026-03-04Day-first to US order
9 October 2026 is written month first in the United States.
Input
09/10/2026 as DD/MM/YYYYResult
10/09/2026 as MM/DD/YYYYUTC date-time for an API
Midnight UTC, which is 8 p.m. on 8 October in New York (EDT).
Input
2026-10-09Result
2026-10-09T00:00:00ZTips and best practices
- If a list has a first number above 12 (25/12/2026), it must be day-first; that is a good clue for picking the source format.
- For file names or sorted rows, prefer YYYY-MM-DD: alphabetical order becomes chronological order.
- The ISO 8601 UTC form fixes midnight in universal time: displayed in a time zone west of Greenwich, it can appear as the previous evening.
- To pull every date out of a long text, use the date extractor first; for a Unix timestamp, use the timestamp converter.
Sources and references
- ISO — ISO 8601 date and time format (opens in a new tab)Page in English
- G. Klyne, C. Newman, RFC 3339 — Date and Time on the Internet: Timestamps (opens in a new tab), RFC Editor, 2002Page in English
- Unicode CLDR — Calendars, dates, weeks and locale conventions (opens in a new tab)Page in English
Frequently asked questions
Why doesn’t the tool detect the format by itself?
Because any date whose day and month are both 12 or less is ambiguous: 03/04/2026 can be 4 March or 3 April. An explicit choice avoids a silent mistake.
What is the ISO 8601 date format?
The extended calendar date format of ISO 8601 is YYYY-MM-DD, for example 2026-10-09. The standard also defines forms with a time, such as 2026-10-09T14:30:00Z.
Are two-digit years accepted?
No. 10/09/26 is rejected because 26 could mean 1926 or 2026. Enter the full year.
Can I type a date with dots, such as 09.10.2026?
Yes. For DD/MM/YYYY and MM/DD/YYYY, dots and hyphens are accepted as separators. The result always uses slashes for these two formats.
What happens to the time in a full ISO date-time?
It is ignored: only the YYYY-MM-DD part is read. 2026-10-09T23:30:00+02:00 gives 9 October 2026, with no time-zone conversion.
Why is 02/29/2025 rejected?
2025 is not a leap year. February only has 29 days in years divisible by 4, except century years not divisible by 400.
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