Why your Word template’s formatting breaks with mail merge (and how to keep it)

You built the template carefully. The date reads "October 22, 1995", the amount reads "$12.00", everything is in the right font. Then you run a mail merge from Excel and the output says "1995-10-22 00:00:00" and "12.00". Nothing is broken. This is documented behaviour, and understanding why it happens tells you both how to fix it and when to use a different tool.

What actually goes wrong

Microsoft documents the failure precisely, in its support article on merging from an Access or Excel data source (support.microsoft.com/en-us/topic/date-phone-number-and-currency-fields-are-merged-incorrectly-when-you-use-an-access-or-excel-data-source-in-word-34131aae-dddb-98a1-bd58-6b89994a357e). The documented symptoms:

• Dates merge in a raw form such as "1995-10-22 00:00:00" instead of the format shown in your spreadsheet.
• Currency merges as a bare number such as "12.00", with no currency symbol.
• Phone numbers merge mangled, in the documented example as "-7081234567.00".

The article states the rule directly: "If you format the data in the data source, the formatting is not retained when you merge." That single sentence is the whole story.

Why: the formatting was never in the data

In a spreadsheet, what a cell contains and what a cell shows are two different things. The cell stores a raw value: a date is a timestamp, an amount is a number. The "$12.00" you see is a display format painted over that value by the spreadsheet. Mail merge connects to the data, not to the display. So Word receives the raw value, and the raw value is what lands in your letter.

This is not a bug in your template and no amount of reformatting the spreadsheet will change it. The formatting has to be reapplied on the Word side, at the point where the value enters the document.

The documented fix: field codes and picture switches

Word’s merge fields are field codes, and field codes accept formatting instructions called picture switches. Microsoft’s documented fix for the date problem is to edit the field code by hand and add a switch, for example:

With that switch, the raw timestamp renders as "October 22, 1995". Numeric switches do the same job for currency and phone numbers. The fix works, and it is worth knowing. It is also worth being honest about what it costs.

• You are editing field codes by hand, inside toggled field-code view, in syntax most Word users have never seen.
• Every date, currency and phone field in the template needs its own switch.
• The template now carries invisible logic. A colleague who opens it sees a normal document and has no idea the switches are there until one is deleted and a merge quietly regresses.

When mail merge is still the right tool

Mail merge deserves a fair statement of its strengths. It is built into Word and free. It runs locally, which keeps the data on your machine. And for true bulk personalization from one clean structured source, such as Excel, Outlook contacts or a database, producing letters, labels, envelopes or email, it is exactly the right tool. If you send three hundred identical letters that differ only in name and address, and your list is already clean, set up the merge, add the picture switches once, and use it.

The mismatch appears when offices stretch mail merge to one-at-a-time document production. Then the tool’s assumptions stop holding: the data must already be structured, so someone retypes values from IDs and scans into a spreadsheet first; there is no per-value review, the merge fills everything and any retyping error rides straight into the output; and the format problem above needs field-switch surgery in every template.

The in-place alternative

For one-document-at-a-time work there is a different approach: fill the existing document directly, instead of merging raw data into it through fields. This is what Run Done does. You upload the Word document you already use, in .doc or .docx, and add the materials you have: photos, scans, other documents or pasted text. The software reads the materials and enters the data in the right places. Because values are written into the document in place rather than pulled through merge fields, the surrounding formatting is simply never touched: fonts, headers, numbering, spacing and layout stay exactly as you set them, with no field codes and no switches to maintain. Values come only from the materials you supplied; a value that cannot be found leaves the field empty. You review every entered value, correct anything you want, and download a finished Word file.

The short version

• Mail merge loses your formatting because it merges raw values; the display format lives in the spreadsheet and does not travel. Microsoft documents this plainly.
• The documented fix is picture switches in the field codes, added by hand, one per field. It works and it is maintenance.
• Use mail merge for true bulk from one clean spreadsheet. For one-at-a-time documents filled from real-world materials, fill the document in place and keep the review.