What an index does and when you need one
An index in Word is a list of terms and the page numbers where they appear in your document. Word scans your document for marked terms, collects them alphabetically, and generates a page that readers can use to find topics quickly. You build it in two steps: mark the terms you want indexed as you write or edit, then insert the index itself at the end of the document.
You need an index when your document is long enough that readers can't scan it easily — typically 20 pages or more. A table of contents shows chapter and heading structure; an index shows where specific topics live. They serve different purposes. A technical manual, a research paper, or a policy document benefits from an index. A short report or letter does not.
The index is generated automatically from your marks, so if you add or delete pages later, you can update the index in seconds rather than rebuilding it by hand. This is one of the practical reasons to use Word's built-in tools instead of typing an index manually.
Key Takeaways
- Mark index terms as you write by selecting the word, pressing Alt+Shift+X, and choosing how you want it to appear in the index.
- You can mark the same term multiple times throughout your document, and Word will collect all the page numbers automatically.
- Insert the index at the end of your document by placing your cursor where you want it, then going to References > Index and choosing a style.
- After you add or delete pages, right-click the index and select Update Field to refresh all page numbers without retyping anything.
How to mark terms for the index
Open your document and find the first term you want readers to be able to look up. Select that word or phrase by clicking and dragging across it. Then press Alt+Shift+X on your keyboard. A dialog box titled "Mark Index Entry" will open.
The term you selected appears in the "Main entry" field. You can edit it here if you want the index to show a different version — for example, if you selected "database" but want the index to read "databases" instead. Leave it as is if the selection is correct. Click the "Mark" button to mark this single instance, or click "Mark All" if you want Word to find and mark every occurrence of that term in the entire document. Use "Mark All" carefully: it marks exact matches only, so "database" and "databases" are treated as separate terms.
The dialog stays open so you can move to the next term. Close it when you are finished marking. As you mark terms, Word adds hidden codes to your document. You can see these codes if you press Ctrl+* (Ctrl+Shift+8 on some keyboards), but you do not need to see them to work with the index.
Creating subentries and cross-references
An index can be flat — just a list of terms — or it can be hierarchical, with main terms and subtopics underneath them. If you are indexing a document about cars, you might want "Engines" as a main entry with "diesel," "electric," and "gasoline" as subentries underneath it.
To create a subentry, select your term and press Alt+Shift+X. In the Mark Index Entry dialog, type the main term in the "Main entry" field and the subterm in the "Subentry" field. For example, Main entry: "Engines" and Subentry: "diesel". Click Mark. When the index is generated, "diesel" will appear indented under "Engines" with its own page numbers.
You can also create cross-references that point readers from one term to another — for example, "See also: Hybrid vehicles" under the "Electric engines" entry. In the Mark Index Entry dialog, select the "Cross-reference" radio button and type the term you want to reference. This is useful when readers might search for a topic under a different name.
Inserting the index into your document
Place your cursor at the end of your document or wherever you want the index to appear — usually on its own page after the main content. Go to the References tab in the ribbon at the top of Word. Click the Index button. A gallery of index styles will appear.
Choose a style that matches your document. "Automatic Table" creates a straightforward two-column layout. "Modern" uses a cleaner design with less spacing. "Fancy" adds a colored background. Click the style you prefer. Word scans all your marked terms, sorts them alphabetically, collects the page numbers, and inserts the finished index at your cursor position.
The index appears as a field — a special object that Word can update automatically. It is not regular text, so you cannot edit it by typing. If you need to change how it looks, delete it and insert a new one with a different style, or right-click it and choose "Edit Field" to adjust the underlying settings.
Updating the index after you edit your document
After you add, delete, or move content, the page numbers in your index become outdated. You do not need to rebuild it. Right-click anywhere in the index and select Update Field. A dialog will ask whether you want to update page numbers only or the entire index. Choose "Update entire index" to catch any new terms you marked and any terms you deleted.
Word rescans the document, recounts pages, and refreshes all the numbers in seconds. This is why marking terms as you write is worth the small effort — it saves you from manually checking page numbers later.
If you make major structural changes — moving whole sections around or adding chapters — update the index before you print or share the document. Readers will notice if page numbers are wrong, and it undermines trust in the document.
Troubleshooting common index problems
If a term you marked does not appear in the index, check that you actually clicked "Mark" or "Mark All" in the dialog. Selecting text and opening the dialog is not enough — you must confirm the mark. Also check that the term is spelled exactly as you want it to appear. Word treats "Database" and "database" as different entries.
If your index shows page numbers that seem wrong, your document may have multiple sections with different page numbering — for example, if front matter uses Roman numerals and the main text uses Arabic numerals. Word handles this correctly, but the index will reflect it. This is not an error; it is accurate.
If you delete a marked term from your document but it still appears in the index, update the index again. Word only removes entries when you update after deletion. If the index still shows the old term, the mark may still be in the document as hidden code. Press Ctrl+* to show hidden marks and delete any orphaned codes manually.
Frequently Asked Questions
Can I mark a phrase instead of a single word?
Yes. Select the entire phrase you want to index, then press Alt+Shift+X. Word treats it as a single entry. You can also use the Main entry and Subentry fields to break a phrase into parts — for example, Main entry: "Cloud computing" and Subentry: "security" to create a hierarchical structure.
What happens if I mark the same term with different spellings?
Word treats them as separate entries in the index. "Database," "database," and "Databases" will each get their own line with their own page numbers. To avoid this, be consistent with capitalization and spelling as you mark terms, or use the "Mark All" button to mark every instance of a term the same way at once.
Can I delete the index and create a new one if I change my mind about the style?
Yes. Click anywhere in the index and press Delete. The marked terms stay in your document — only the generated index is removed. Mark any new terms you want, then insert a new index with a different style using the References tab. Your marks are preserved.
Do I have to mark every single instance of a term, or just the first one?
You can mark just the first instance if you want the index to show only that page number. Or use "Mark All" to mark every occurrence and show all page numbers where the term appears. The choice depends on your document — a technical manual might list every page where a term is mentioned, while a narrative document might list only the main discussion.