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TheSpreadFix

Standardize Date Formats in Excel & CSV

Dates in one column often arrive in several formats — 25/03/2024, 2024-03-26, 03/27/2024, 28 Mar 2024. TheSpreadFix detects every format, works out whether numeric dates are day-first or month-first from the evidence in your file, asks you when it can't tell, and converts everything to YYYY-MM-DD.

Drop a CSV or Excel file here

.csv, .xlsx, .tsv

Your file stays on your device. It's read and cleaned in your browser — nothing is uploaded.

How it works

  1. Step 1

    Upload the file

    Date columns are detected from their names and contents.

  2. Step 2

    Check the formats found

    The report lists each format and how many dates don't match the most common one.

  3. Step 3

    Confirm & convert

    Confirm day-first or month-first if needed, preview, and convert to YYYY-MM-DD.

What it checks and fixes

Mixed formats

YYYY-MM-DD, DD/MM/YYYY, MM/DD/YYYY, DD-MM-YY, DD.MM.YYYY, “12 Jan 2024” and “Jan 12, 2024” in the same column.

Ambiguous dates

Values like 03/04/2024 that could be 3 April or March 4 — counted and never guessed.

Conflicting sources

Columns where some dates are clearly day-first and others clearly month-first, which usually means merged sources.

Invalid dates

Impossible values (31/02/2024, 2023-02-29) and text such as “next Tuesday”, listed for manual review.

The day-first vs month-first problem

India, the UK and most of the world write dates day-first (25/03/2024); the US writes them month-first (03/25/2024). When a date's day is 13 or more, the order is obvious. When both parts are 12 or less — 03/04/2024 — it's genuinely ambiguous, and a tool that guesses will silently shift dates by months.

TheSpreadFix uses the unambiguous dates in the column as evidence. If every clear date is day-first, the column is treated as day-first — and the report tells you so. If there's no evidence, or the evidence conflicts, it asks you to choose before converting anything.

Why YYYY-MM-DD?

YYYY-MM-DD (ISO 8601) can't be misread in any country, sorts correctly as text, and is accepted by virtually every database, CRM and import tool. It's the safest format for moving data between systems; you can always display dates differently in Excel afterwards with a custom number format.

InputSettingOutput
25/03/2024detected day-first2024-03-25
03/25/2024detected month-first2024-03-25
03/04/2024you chose day-first2024-04-03
12 Jan 2024—2024-01-12
05/05/24—2024-05-05
2024-02-29 14:30—2024-02-29 14:30

Two-digit years and times

Two-digit years from 00–49 become 2000–2049 and 50–99 become 1950–1999. Times after a date are kept (midnight times such as 00:00:00 are dropped, since they're usually an artefact of Excel's date storage).

Frequently asked questions

Can I convert to DD/MM/YYYY instead?

The cleaner converts to YYYY-MM-DD, the format least likely to be misread. Other output formats are supported by the engine and will be selectable in a future update.

Which month names are recognised?

English month names and abbreviations (Jan, January, Sept…).

What happens to values that aren't dates?

They're left unchanged and listed as unreadable dates so you can fix them by hand.

Why are some dates left unchanged?

Ambiguous dates are only converted after you confirm day-first or month-first. Nothing is guessed.