Error guides / Any CSV importer

Any CSV importer

“Excel changed my CSV and now it will not import”

Opening a bank CSV in Excel to "just take a look" is one of the most reliable ways to break it. Excel does not open a CSV — it interprets one, converting anything that resembles a number or date into its own idea of that value. Save afterwards and those interpretations become your data.

Updated Aug 2026 · Applies to Any CSV importer

Symptoms

  • Account or reference numbers lost their leading zeros
  • Dates changed format, or turned into serial numbers like 45870
  • Long card numbers became scientific notation such as 4.53E+15
  • The file imported fine before you opened it and fails afterwards

What actually causes it

Cause 1

Automatic type conversion on open

Excel decides on open that 00123 is the number 123, that 08/01/2026 is a date in the local format, and that a 16-digit card number is a float. Nothing warns you, and saving writes the converted values back.

Cause 2

Locale-driven date rewriting

The same file opened on a US machine and a European one produces different dates, because Excel applies the operating system's date order when it interprets and again when it writes.

Cause 3

Delimiter changed on save

In locales that use a comma as the decimal separator, Excel saves CSV with semicolons, so a file that arrived comma-delimited leaves semicolon-delimited.

How to fix it

  1. If you still have the original download, go back to it — a converted file cannot be reliably reversed, because the original digits are gone rather than hidden.
  2. Drop the file into the checker below to see what shape it is in now: delimiter, column alignment and blank rows are all reported.
  3. To inspect a CSV safely in future, use Excel's Data → From Text/CSV import (which lets you set every column to Text) rather than double-clicking the file.
  4. Better still, do not open it at all — the fixer here reads the file without altering it.
Any importer“The download worked last month and fails now”Actual Budget / Firefly III“My bank CSV will not map correctly in Actual Budget”Lloyds / Nationwide / NatWest“My UK bank CSV will not map correctly”Any importer“Accented payee names import as garbled characters”

Skip the manual edit — fix it automatically

The checker reports the file's current delimiter and column structure, which is exactly what you need to know after Excel has had a turn with it. Free, no signup, no upload.

Open the fixer

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