Excel Keeps Changing Numbers to Dates: stop it

Type 1/2, 3-4 or SEPT1 and Excel decides it is a date. Fractions, ratios, product codes and gene names all get mangled. Here is why and how to stop it.

Why

Excel guesses the type of everything you type. Anything that looks like a date becomes one, and the original text is gone.

Fix 1: format the cells as Text first

1. Select the column before typing.
2. Press Ctrl + 1 › Text › OK.
3. Now type 1/2. It stays 1/2.

Fix 2: an apostrophe

Type '1/2. The apostrophe tells Excel “this is text” and does not show in the cell.

Fix 3: for imported files

Do not double-click the CSV. Use Data › From Text/CSV and set the column type to Text before loading. Steps: CSV to Excel.

Get the original back

If you typed 1/2 and got 01-Feb, press Ctrl + Z straight away. Later than that, Excel only has the date now. Retype it.

I want a real fraction

Type 0 1/2 (zero, space, one slash two). Excel stores 0.5 and shows ½.

Check it worked

Click the cell. The formula bar shows exactly what you typed, and the cell is left-aligned (text) rather than right-aligned (number/date).

Related annoyances

Excel also turns long numbers into 1.23E+15 and strips leading zeros. Same fix: Text format before typing.