How to Add Spell Check in Microsoft Word (And Make It Work the Way You Need)

Spell check in Microsoft Word sounds like a simple on/off switch — but it behaves differently depending on your version of Word, your operating system, the document type you're working in, and how your settings have been configured over time. Understanding how spell check actually works in Word helps explain why it sometimes seems to stop working, ignore errors, or behave inconsistently across documents.

How Spell Check Works in Word

Word uses two overlapping systems: automatic spell check (the red squiggly underlines that appear as you type) and manual spell check (the full document review you trigger through the Review tab or by pressing F7).

Both systems rely on the same underlying proofing language dictionaries — Word checks your text against a built-in dictionary for whatever language is assigned to that text. This is an important detail: Word assigns proofing languages at the text level, not just the document level. A single document can contain paragraphs set to different languages, and Word will check each section against the appropriate dictionary.

When spell check seems to miss errors, it's often because:

• The text has been marked "Do not check spelling or grammar"
• The proofing language for that text block is set to something unexpected
• The spelling and grammar check has been disabled in Word's options
• The document was created or pasted from a source that carried over different formatting or language settings

How to Enable or Re-Enable Spell Check in Word

On Windows (Microsoft 365 / Word 2016, 2019, 2021)

1. Open Word and go to File → Options
2. Click Proofing in the left sidebar
3. Under When correcting spelling and grammar in Word, make sure the following boxes are checked:
   • ✅ Check spelling as you type
   • ✅ Mark grammar errors as you type
   • ✅ Check grammar with spelling
4. Click OK

If the boxes are already checked but spell check still isn't working, the issue may be at the text level. Select all text with Ctrl + A, then go to Review → Language → Set Proofing Language and uncheck "Do not check spelling or grammar".

On Mac (Microsoft 365 / Word for Mac)

1. Open Word and go to Word → Preferences from the menu bar
2. Click Spelling & Grammar
3. Enable Check spelling as you type and Check grammar as you type
4. Close the preferences window

The language settings path on Mac is slightly different: go to Tools → Language to manage proofing language assignments at the text level.

In Word for the Web

Word Online has a more limited proofing toolset. Spell check runs automatically and cannot be fully disabled or reconfigured the way desktop Word can. If you're seeing inconsistent behavior in Word Online, it's worth knowing that the web version doesn't support all proofing customizations available in the desktop app — custom dictionaries, grammar detail settings, and language-level controls are largely desktop-only features.

Adding and Managing Custom Dictionaries 📖

Word's built-in dictionary won't recognize every word you use — technical jargon, product names, company-specific terminology, and proper nouns will often get flagged. This is where custom dictionaries come in.

To add a word to your custom dictionary, right-click any red-underlined word and select "Add to Dictionary". That word is then stored in your personal custom dictionary and won't be flagged again across any Word document.

To manage your custom dictionary directly:

• Go to File → Options → Proofing → Custom Dictionaries
• You can edit the dictionary list, add words manually, or import a .dic file

This matters if you're working in a specialized field where standard dictionaries produce a lot of false positives. A heavily flagged document can make it harder to spot real errors.

Why Spell Check Behaves Differently Across Documents

Several factors cause spell check to work differently from one document to another:

Documents created from templates, converted from PDF, or assembled by copy-pasting from multiple sources are especially prone to mixed proofing settings — because formatting and language attributes travel with the text.

Grammar Check vs. Spell Check

These are separate features in Word, though they're controlled from the same settings panel. Spell check flags words not found in the active dictionary. Grammar check analyzes sentence structure, punctuation, and style — and in Microsoft 365, this layer has expanded significantly with AI-assisted suggestions under the Editor feature.

If you're using Microsoft 365, you'll see an Editor Score panel that goes well beyond traditional spell check into clarity, conciseness, and formality suggestions. This is a meaningfully different experience from standalone Word 2016 or 2019, where grammar checking is more limited and rule-based.

The Variables That Determine Your Experience

How well spell check works for any individual user depends on a combination of factors that interact in non-obvious ways:

• Word version — Microsoft 365 subscribers get ongoing updates to the proofing engine; perpetual license users (2016, 2019, 2021) have static feature sets
• Language and region settings — English (US) and English (UK) dictionaries treat the same words differently; mixed-language documents add another layer of complexity
• Document history — how the document was created, where text was pasted from, and whether protection settings are active
• Custom dictionary state — a heavily populated custom dictionary can suppress legitimate errors if words were added incorrectly
• Operating system — Word for Mac and Word for Windows share core features but differ in menu paths, keyboard shortcuts, and some proofing behaviors 🖥️

Getting spell check working reliably often involves tracing back through which of these variables is affecting a specific document — rather than a single universal fix. The right approach depends on which combination of settings, Word version, and document type you're actually dealing with.