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Choose your CSV
Upload a comma-separated UTF-8 file with named columns.
Developer Tools
CSV Date Column Fixer
Fix Excel serial numbers and multiple CSV date columns with an explicit format for each column.
Select one or more date columns. Every selected column has its own source format, so ambiguous dates are never guessed.
Your file stays in your browser and is never uploaded.
Data handling
Storage and export controls
- Retention
- The tool's working state is kept only while this page is open. Inputs and results are not saved to persistent storage by Got A Tool.
- Export
- The tool may prepare a result after you run it. It downloads or copies it only when you choose that action.
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How it works
Fix multiple date columns without guessing
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Set each source format
Select every date column and choose its own MM/DD, DD/MM, or YYYY-MM-DD source format.
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Review and download
Download YYYY-MM-DD conversions while cells needing review remain unchanged.
Example
Keep mixed source columns explicit.
A US order-date column and a UK delivery-date column can both contain 03/04/2026. Choose MM/DD/YYYY for the first and DD/MM/YYYY for the second. The output becomes 2026-03-04 and 2026-04-03, without any row-by-row guessing.
What stays unchanged
All non-date columns remain as they were. Invalid dates are identified by source row and column, then kept unchanged in the downloaded CSV for review.
Questions
CSV date fixing questions
Can one CSV use more than one date format?
Yes, when each format belongs to a different selected column. Choose the source format for every column independently; the tool never infers a format from another column or another row.
What happens to an ambiguous date?
It follows the format you selected for that exact column. For example, 03/04/2026 becomes March 4 with MM/DD/YYYY and April 3 with DD/MM/YYYY.
Are Excel serial dates supported?
Yes. Excel serial numbers and ISO YYYY-MM-DD values are recognized in every selected date column.
What happens to invalid dates?
They are listed with their row and column, then stay unchanged in the downloaded file so no uncertain value is silently rewritten.
Is my CSV uploaded?
No. Reading, conversion, and CSV creation happen locally in your browser.
Practical guide
Read the CSV and Excel safety guide
Check identifiers, spreadsheet formulas, and file structure before you open a reviewed CSV in a spreadsheet.
Open the guide →Keep working
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