Date List Converter & Validator
Convert lists of calendar dates between ISO, day/month/year and month/day/year formats. Flag invalid dates, weekdays and repeated dates without guessing ambiguous input.
Settings
Try the example or enter your own settings.
Using Date List Converter & Validator
Convert lists of calendar dates between ISO, day/month/year and month/day/year formats. Flag invalid dates, weekdays and repeated dates without guessing ambiguous input.
- Paste dates on separate lines or open a UTF-8 text file.
- Select the exact source format and desired output format. No date order is guessed.
- Convert, review invalid and duplicate dates, then export the CSV table or complete JSON report.
Example
Try the included editable example. Select the exact source format and desired output format. No date order is guessed.
Questions & answers
How are ambiguous dates handled?
You choose the source format explicitly. In DD/MM/YYYY, 03/04/2026 means 3 April; in MM/DD/YYYY it means March 4.
What makes a date invalid?
The tool requires exact padded formats and real Gregorian calendar dates with years 0001–9999. Impossible dates such as 2025-02-29 stay flagged in the report.
Does it convert timezones?
No. These are calendar-only dates. Weekdays are calculated using UTC internally to avoid changing dates with the device timezone.
Can I process a CSV column?
Copy the date column into the input with one date per line. Whole multi-column CSV input is not parsed by this tool.
Are duplicate dates removed?
No. Every nonblank source line is retained with its original line number. A separate duplicate summary shows repeated valid dates.
What is saved or uploaded?
Processing is local. Nothing is automatically saved. Export CSV for spreadsheet review or JSON for complete results; the input limit is 100,000 characters and 2,000 nonblank dates.
Related tools
A useful next step for your task.
ConvertersISO Week Date ConverterConvert a calendar date into an ISO week date, or convert a week date back to a calendar day.
Everyday CalculatorsDate Difference & Working DaysCount calendar days and working days between two dates. Choose working weekdays and exclude your own holiday dates.
Developer & DataUnix Timestamp ConverterConvert Unix seconds or milliseconds to UTC and local dates, or dates to timestamps. Includes current time, exact millisecond precision, batch…
ConvertersUnit ConverterRecommendedConvert length, mass, temperature, area, volume, speed, time and digital storage. Strict inputs, batch reports and clearly labeled US, imperial…
Help improve this tool
Report a problem or suggest an improvement
Describe the issue without pasting private tool input. Feedback goes to our admin inbox.