You export a CSV from a UK system and double-click it in US Excel — 28/05/2026 suddenly looks like May 28, or something even stranger. The file isn't corrupt. Excel is guessing your date format based on your computer's locale.
This short guide covers why that happens, how to import CSV correctly, and how to batch-fix dates that are already wrong. For the full walkthrough with examples, see the official guide: — everything runs locally in your browser:
1. — check before you commit
Enter a single date like 03/04/2025 and see US vs UK interpretations side by side — no guessing.
Best for: visa forms, contracts, anything where the exact day matters.
3. . Order matters — wrong dates baked into JSON propagate through your entire pipeline.
Quick FAQ
Quick FAQ
Q: Why did my dates turn into numbers like 44927?
A: Excel stores dates as serial numbers internally. Date Format Fixer converts them back to readable dates.
Q: Fix dates first, or convert to JSON first?
A: Fix dates first. Bad dates in JSON pollute validation and reporting downstream.
Summary
| Scenario | What to do |
|---|---|
| Not imported yet | Excel "import from text"; set date column to Text or ISO |
| Team data exchange | Agree on YYYY-MM-DD |
| Already wrong |
If you also work with ChatGPT output, JSON, or CSV pipelines, FormatList has JSON Repair, CSV converters, and more at .
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