Missing hyphens in compounds

When a number plus a unit acts together as a modifier before a noun, connect the parts with hyphens: twenty-four-hour service, five-year-old child, seven-foot-tall player.

Below are concise rules, quick diagnostics, and many copy-and-paste corrections for work, school, and casual writing.

Quick answer

If a number + unit directly modifies a noun and appears before it, hyphenate the whole phrase (twenty-four-hour service; five-year-old child). If the phrase follows a linking verb, do not hyphenate (The service is twenty-four hours; The child is five years old).

Before a noun: hyphenate (a three-course meal → three-course).
After a verb: no hyphen (The meal is three courses).
Use numerals or words consistently (24-hour or twenty-four-hour); never add spaces around hyphens.

Core rule: number + unit that modifies a noun gets hyphens

When number + unit (year, hour, foot, page, day, etc.) forms a single adjective placed before a noun, link all parts with hyphens. When the same phrase follows a linking verb or stands alone as a measurement, don't hyphenate.

Adjective before noun → hyphenate: five-year-old child, ten-page report.
Predicate (after verb) → no hyphen: The child is five years old; The report is ten pages.

Wrong: The restaurant provides twenty four hour service.
Right: The restaurant provides twenty-four-hour service.
Wrong: She bought a five year old car.
Right: She bought a five-year-old car.
Wrong: They went on a ten days vacation.
Right: They went on a ten-day vacation.

Hyphenation with numerals and spacing (24-hour vs 24 hour)

Numerals follow the same hyphen rules as spelled-out numbers: 24-hour shift, 3-year warranty, 7-foot-tall statue. Never insert spaces around the hyphen.

No spaces around hyphens: write 24-hour (not 24 - hour or 24 hour).
Numerals are often clearer in technical or compact text: 3-year-old, 24/7, 9-to-5.
When numbers are spelled out, hyphenate too: twenty-four-hour.

Wrong: We offer 24 hour delivery.
Right: We offer 24-hour delivery.
Wrong: The three month plan is cheaper.
Right: The three-month plan is cheaper.
Wrong: She works nine - five shifts.
Right: She works nine-to-five shifts.

Predicate vs modifier: when NOT to hyphenate

If the number phrase is the predicate (after a linking verb) and not directly modifying a following noun, do not hyphenate. If you need a modifier before the noun, hyphenate; otherwise, leave it unhyphenated after the verb or rephrase.

Before noun → hyphenate: a two-week internship.
After verb → no hyphen: The internship lasts two weeks.
If a hyphenated stack looks awkward, rephrase: service available 24 hours a day.

Wrong: Their stay was ten-day.
Right: Their stay lasted ten days.
Wrong: He is a seven foot tall player.
Right: He is a seven-foot-tall player.
Wrong: He is seven-foot-tall.
Right: He is seven feet tall.

Real usage and tone: signage, marketing, and formal writing

Headlines and signage sometimes drop hyphens for space or branding (24 hour fitness). In formal documents-resumes, reports, academic prose-hyphens improve clarity and read as professional.

Marketing: brevity may omit hyphens in headlines; in body copy, hyphenate modifiers.
Resumes/reports: hyphenate to signal precision (three-year partnership; ten-page report).
Casual messages: small hyphens help readability, even in texts and reviews.

Usage: Sign: 24 hour parking. Editorial: 24-hour parking.
Usage: Ad headline: Five Star Dining. Body copy: five-star dining experience.
Work - Usage: Resume wrong: five year experience. Better: five years' experience or five years of experience.

Try your own sentence

Test the phrase in context: place it before and after the noun or verb to see which form reads correctly.

Examples you can copy: Work, school, and casual fixes

Copy these wrong → right pairs as templates for emails, assignments, and social posts.

Work - Wrong: The restaurant provides twenty four hour customer support to corporate accounts.
Work - Right: The restaurant provides twenty-four-hour customer support to corporate accounts.
Work - Wrong: We launched a three month pilot with our vendors.
Work - Right: We launched a three-month pilot with our vendors.
Work - Wrong: Please submit a ten page market analysis by Friday.
Work - Right: Please submit a ten-page market analysis by Friday.
School - Wrong: The restaurant provides two week internship placements to culinary students.
School - Right: The restaurant provides two-week internship placements to culinary students.
School - Wrong: Submit a ten page report on dining trends.
School - Right: Submit a ten-page report on dining trends.
School - Wrong: She conducted a five year study of menu changes.
School - Right: She conducted a five-year study of menu changes.
Casual - Wrong: He has six pack abs now.
Casual - Right: He has six-pack abs now.
Casual - Wrong: We left after a three hour wait.
Casual - Right: We left after a three-hour wait.
Casual - Wrong: She works a nine to five schedule.
Casual - Right: She works a nine-to-five schedule.

Rewrite help: quick fixes when hyphens clutter the sentence

Checklist: 1) Is number+unit directly before a noun? Hyphenate. 2) Is it after a verb? Don't hyphenate. 3) If stacked hyphens are hard to read, rewrite the phrase.

Swap hyphens for a prepositional phrase: a study that lasted five years; training that lasts five weeks.
Use synonymous set phrases: round-the-clock service or service available 24 hours a day.
When multiple modifiers stack, reorder or use numerals for clarity: 20-year, full-time role.

Rewrite:
Wrong: The restaurant provides twenty four hour service. Fix: The restaurant provides twenty-four-hour service. Or: The restaurant offers round-the-clock service.
Rewrite:
Wrong: We run a five week training. Fix: We run a five-week training. Or: We run training that lasts five weeks.
Rewrite:
Wrong: The menu features a three course tasting menu. Fix: The menu features a three-course tasting menu. Or: The menu includes a three-course tasting.
Rewrite:
Wrong: She has a 20 year, full time role. Fix: She has a 20-year full-time role. Or: She has worked full time for 20 years.

Memory tricks and quick checks

Two quick rules: Before = Hyphen and After = No hyphen. Replace the phrase with a single-word substitute-if that sounds natural, hyphenate.

'Before = Hyphen' example: a ten-page paper.
'After = No hyphen' example: The paper is ten pages.
If unsure, rewrite to avoid ambiguity rather than guess punctuation.

Test: Replace 'three-course' with 'one-course'-if it reads like a single adjective, hyphenate.

Similar mistakes to watch for (spacing, en dash, plurals, possessives)

Fixing hyphens can create other errors. Watch ranges, plurals, and possessives.

Range → use an en dash or 'to': 2010-2015 or 2010 to 2015 (print style prefers an en dash).
Plural modifier: five-year-olds (noun) vs a five-year-old child (adjective + noun).
Possessive years: prefer five years' experience or five years of experience rather than five-year experience.
Prefixes: follow your style guide for compounds (well-known vs well known).

Usage: Wrong: The conference runs 2018-2019.
Right: The conference runs 2018-2019 or 2018 to 2019.
Usage: Wrong: five year olds.
Right: five-year-olds (as a noun) or a five-year-old child (as adjective + noun).
Work - Usage: Wrong: five year experience.
Right: five years' experience or five years of experience.

FAQ

Do I hyphenate 'twenty four hour'?

Yes, when it modifies a noun before the noun: 'twenty-four-hour service' or '24-hour service.' If it follows a verb, write 'twenty-four hours' without hyphens.

Is it 24 hour or 24-hour?

Use 24-hour before a noun (a 24-hour pharmacy). After a verb, write 'The pharmacy is open 24 hours.'

Should ages be hyphenated (five year old)?

Hyphenate ages used as modifiers before nouns: 'a five-year-old student.' Do not hyphenate after a verb: 'The student is five years old.'

When do I use an en dash instead of a hyphen?

Use an en dash for ranges (2010-2015 or 2010 to 2015). Use a hyphen for compound modifiers (three-year study). In plain text people sometimes use a hyphen for ranges, but editorially prefer an en dash.

How can I check hyphenation quickly?

Ask: Is the number phrase directly before a noun and acting as a single modifier? If yes, add hyphens. If unsure, rewrite the sentence (e.g., 'service available 24 hours a day') or paste the sentence into a grammar tool for an instant suggestion.

Check one sentence now

When editing for work or school, prefer hyphenation for number-based modifiers before nouns to keep your writing crisp and professional. If a phrase feels awkward, rephrase rather than force hyphens.