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.
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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