Excel removes leading zeros from your CSV — how to keep them

You open a CSV in Excel and employee ID 007 has become 7, the ZIP code 02134 is now 2134, and order number 12345678901234567890 shows as 1.23457E+19. Excel is trying to be helpful: anything that looks like a number is converted into one.

Why the zeros disappear

When Excel opens a CSV, it inspects each value and converts anything numeric-looking into a number. Mathematically, 007 and 7 are the same, so the leading zeros are discarded.

But in real data, many of these values aren’t quantities at all — they are labels that happen to contain digits:

• ZIP and postal codes, employee and student IDs, product codes
• Phone numbers with a leading 0
• Account, card and order numbers

Long numbers are even more at risk

Excel stores numbers with 15 significant digits of precision. Convert a 16- or 20-digit ID into a number and every digit after the 15th becomes 0; Excel then displays it in scientific notation, like 1.23457E+19. If you save the file in that state, the original number is gone for good. Credit-card-length numbers and long order IDs are frequent victims.

Fix 1: Import the columns as text in Excel

1. In Excel, choose Data → From Text/CSV and pick the file.
2. Click Transform Data to open the Power Query editor.
3. For each column that must keep its zeros, click the type icon in the column header and choose Text, then Replace current.
4. Click Close & Load.

This is precise, but tedious with many columns and needs repeating for every file.

Fix 2: Convert CSV to XLSX without changing values

The CSV to XLSX converter types values conservatively, so nothing is silently altered:

• Only unambiguous numbers such as 42 or 3.14 become numbers.
• Values with leading zeros, like 007, stay text.
• Numbers longer than 15 digits stay text, exactly as written.
• Formatted values such as 1,234 are kept as they appear.

To keep absolutely everything as text, choose Keep everything as text under Options → Values. The resulting XLSX opens in Excel with every zero in place. The CSV to JSON converter applies the same rules, keeping codes and long IDs as strings.

Fix 3: Exporting from Excel without losing zeros

Cells formatted as Text in Excel (often marked with a small green triangle) are exported exactly as written by the XLSX to CSV converter. Cells that only display zeros through a number format like 000 are exported the way they appear on screen.

Habits that prevent the problem

• Treat codes and IDs as text from the start — you never calculate with them.
• Don’t save a CSV straight after opening it in Excel; you may overwrite it with the damaged values.
• For important data, exchange XLSX files rather than CSV.

Summary

Missing leading zeros come from Excel mistaking codes for numbers. Import the columns as text, or convert the CSV with a tool that types values conservatively. For more on choosing between the two formats, see CSV vs XLSX.