MM/DD/YYYY to ISO 8601 date (YYYY-MM-DD)
CSV exports from US software put the month first. Convert to ISO before importing into a database or sheet so day and month never get swapped.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter date mm/dd/yyyy.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Month, day and year are read in that order; the month must be 1 to 12 and the day must exist in it (leap years included), then YYYY-MM-DD is written.
Example
Inputs: Date MM/DD/YYYY = 12/25/2026. Result: ISO 8601: 2026-12-25; Weekday: Friday.
12/25/2026
2026-12-25
Limits and caveats
- The year must have four digits, so 12/25/26 is rejected.
- A date such as 03/04/2026 is valid either way; the tool always reads it month first.
Questions about this tool
What is the US date 03/04/2026 in ISO form?
Month 03 and day 04, so it becomes 2026-03-04, the 4th of March.
Why convert to ISO before importing?
Spreadsheets may read 03/04 using the computer locale and swap day and month, while YYYY-MM-DD has only one reading.
What if my date is day-first?
Use the DD/MM/YYYY to ISO tool, which reads the day before the month.