Hyphenation Rules: When to Use Hyphens
A position-first method for compounds, numbers, and prefixes.
Quick Answer
Usually hyphenate a temporary compound before a noun: compare a well-known author with the author is well known. Then check the exact term: Merriam-Webster lists long-term as an adjective, so write a long-term lease and the lease is long-term. Use open long term when term is the noun, as in served a long term.
Do not hyphenate a true -ly adverb plus an adjective or participle: a highly rated restaurant. Hyphenate spelled-out numbers such as thirty-two, and use a hyphen when a prefix would otherwise create a different word: re-sign, not resign, when you mean sign again.
First Ask What Kind of Compound It Is
Position is a useful first test, not an absolute law. Established compounds can be open, closed, or hyphenated, so a current dictionary or required house style outranks a memory trick.
This page covers how words combine. To compare the short hyphen with en and em dashes, use the separate hyphen, en dash, and em dash guide. For the role of each mark in a sentence, see the English punctuation overview.
A Practical Hyphenation Decision Table
| Pattern | Working decision | Example |
|---|---|---|
| Temporary compound before a noun | Usually hyphenate the unit | a science-fiction convention |
| Comparable phrase after a noun | Often leave it open | The author is well known. |
| True -ly adverb + adjective or participle | Leave it open | a poorly written memo |
| Spelled-out compound whole number | Join the number parts | thirty-two |
| Number-and-measurement unit before a noun | Hyphenate the unit | a 10-year plan |
| Prefix | Usually close it; hyphenate to prevent misreading or before some capitals and numbers | preexisting, re-sign, pre-2000 |
The words usually and often matter. Merriam-Webster notes that familiar compounds may stay open before a noun and that some established hyphenated compounds retain the mark after the noun.
Four Repairs, with the Reason Exposed
They signed a long term lease.
They signed a long-term lease.
It was a highly-rated restaurant.
It was a highly rated restaurant.
The team proposed a 10 year plan.
The team proposed a 10-year plan.
Please resign the contract tomorrow.
Please re-sign the contract tomorrow.
Test the Boundary, Not Just the Shape
1. A policy lasting five years is a “five-year policy.” Between five and year, choose ___.
2. “The policy is five years old.” Between five and years, choose ___.
3. “a carefully revised proposal” uses a true -ly adverb, so choose ___.
4. The spelled-out number “forty-six” needs a ___.
5. To mean “cover again,” write “re-cover” with a ___.
Live Check: A Missing Hyphen the Engine Did Not Flag
On July 16, 2026, we tested the exact starter sentence below and then the revision using Merriam-Webster's listed adjective long-term. The checker returned no issues for either version.
Manual edit: They signed a long-term lease for the office. Merriam-Webster lists long-term as an adjective, so the dictionary supplies the spelling for this use.
A no-issue result does not decide compound styling. Check the compound in a current dictionary, identify its position, and apply the appropriate rule yourself.
Frequently Asked Questions
Do all two-word modifiers need a hyphen before a noun?
Do compound modifiers lose the hyphen after a noun?
Why is highly rated not hyphenated?
When do numbers take hyphens?
Can the checker decide whether a compound needs a hyphen?
Source-Backed Boundaries
Merriam-Webster's overview of open, closed, and hyphenated compounds documents both the usual before-noun pattern and its exceptions. Its compound-word guide covers prefix attachment, ambiguity, and the fact that some compounds keep a hyphen after the noun.
Merriam-Webster's dictionary lists long-term as an adjective; that exact entry outranks the general before-or-after shortcut. The guide's hyphenated-numbers section directly gives number-and-measurement modifiers and whole numbers such as twenty-one. The MLA Style Center's -ly adverb note directly supports leaving that compound open.
Compound styling can change as usage changes. Merriam-Webster describes an open-to-hyphenated-to-closed path for many compounds, but not as a required three-stage life cycle for every word. When your sentence and a reliable current dictionary disagree with a shortcut, follow the dictionary or the house style required for the document.
A Three-Pass Manual Check
- Look up the compound. If a current dictionary lists the exact term, begin with that spelling instead of rebuilding it from a general rule.
- Mark its job and position. Is it a temporary modifier before a noun, a phrase after the noun, a number unit, or a prefixed word?
- Test the exception. Remove an unnecessary hyphen after a true -ly adverb; add one where a number unit needs grouping or a prefix would create a different word.
This method also prevents overcorrection. A phrase can modify a noun without automatically taking a hyphen, and a compound can remain hyphenated after a noun when established usage supports that form.
Related Guides
- Hyphen, En Dash, and Em Dash – choose the correct horizontal mark.
- English Punctuation Marks – place hyphens in the wider punctuation system.
- Apostrophe Rules – distinguish possession and contractions from word joining.
- View all grammar guides
Check the Sentence, Then Check the Compound
Use the writing studio for sentence-level feedback. For hyphenation, keep the dictionary-and-position pass above in your final edit.
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