Writing numbers correctly isn’t just a grammar issue it’s about clarity, consistency, and knowing your audience. Whether you’re drafting a report, creating website content, or writing a novel, using figures vs. numerals, applying number formatting rules, and knowing when spelling out numbers is preferred can elevate the quality of your writing.
From AP style numbers to the Chicago Manual of Style numbers, every professional format has its own guidelines. But once you understand the core rules and common patterns, writing numbers becomes second nature.
When to Spell Out Numbers and When to Use Numerals
Knowing when to spell out numbers and when to use figures is essential. Generally, numbers zero through nine are spelled out, while 10 and above are written as numerals. However, style guides differ, so always stay consistent with the format you’re following.
Use numerals in data-heavy or technical content, but spell out numbers in narrative or formal prose when it improves flow and readability.
AP Style vs. Chicago Manual of Style Numbers
Different styles mean different rules. Let’s look at the key differences:
| Style Guide | Spell Out | Use Numerals | Notes |
|---|---|---|---|
| AP Style | One through nine | 10 and above | Always use numerals for time, age, money, and dates. |
| Chicago Style | Zero through one hundred | Above 100 | Spell out if not technical; use numerals for precision. |
Sticking to one style throughout your content shows professionalism and avoids confusion.
Hyphenated Numbers and Compound Number Rules
Hyphenated numbers come into play with compound numbers from twenty one to ninety nine. For example: twenty-five students or eighty seven pages.
When a compound number functions as a modifier, hyphenate it: a 10-year-old boy. But if it’s a noun complement, don’t hyphenate: The boy is 10 years old.
Writing Fractions in Sentences
Use hyphenated words for simple fractions: one-third, two-fifths. When a whole number and fraction are combined, numerals are typically used: 3½ cups of flour.
In formal writing, spell out simple fractions unless precision is required especially in scientific or technical writing, where numerals are clearer.
Using Commas in Large Numbers
Commas make numbers easier to read. Always insert commas for numbers 1,000 and above for example: 4,500, 23,000, or 1,200,000.
Avoid commas in years, house numbers, or page numbers: ✅ 2025, 1234 Maple St., Page 35
Writing Time of Day Correctly
Use numerals to write time: 4 p.m., 10:30 a.m.. Lowercase a.m. and p.m. with periods is the standard, and don’t use “o’clock” in professional writing.
Use “noon” and “midnight” instead of 12:00 p.m. or 12:00 a.m. to avoid confusion.
How to Format Decimals and Zero Before Decimal
When writing decimals, always use a zero before the decimal point if the value is less than one. ✅ 0.75 ❌ .75
Keep decimal places consistent usually two digits unless you’re dealing with scientific accuracy or currency formatting.
Writing Amounts of Money the Right Way
Use numerals for money amounts with a currency symbol: ✅ $10 ❌ Ten dollars (unless in formal contracts)
For amounts less than a dollar, write: 75 cents or $0.75 but be consistent throughout your document.
Writing Large Numbers for Readability
Use a combination of numerals and words when dealing with large figures: ✅ 2 million viewers, 5.3 billion dollars
Avoid writing it out entirely: Two million three hundred thousand it’s clunky and hard to scan.
Writing Dates and Decades the Smart Way
Dates should follow this clear format: ✅ October 4, 2025 ❌ 4th of October, 2025
For decades, write: ✅ the 1990s or the ’90s but don’t add an apostrophe before the “s”: ❌ the 90’s
Capitalize named decades like the Roaring Twenties if it’s a proper noun.
Essential Number Formatting Rules
Stick to these quick principles:
- Don’t start a sentence with numerals spell them out or restructure the sentence.
- Avoid combining words and numerals in one phrase: ten 3-year-olds becomes confusing.
- Be consistent with your formatting especially in lists and tables.
Common Mistakes to Watch Out For
- Mixing styles in the same document
- Using a decimal without a leading zero
- Omitting hyphens in compound numbers
- Incorrect use of commas in large numbers
- Confusing AM/PM and noon/midnight
Quick Reference Table
| Situation | Use | Example |
|---|---|---|
| Numbers 0–9 | Spell out | three cats |
| 10 and above | Use numerals | 14 students |
| Time of day | Numerals with a.m./p.m. | 6:30 p.m. |
| Money | Numerals + currency symbol | $25.75 |
| Decimals | Numerals with leading zero | 0.45 |
| Fractions | Hyphenated words or mixed | one-half / 2½ hours |
| Large numbers | Numerals + word form | 2 million people |
| Dates and decades | Month first / ’90s format | October 4, 2025 / the ’90s |
FAQs
Should I write 0.5 or .5?
Always write 0.5 never drop the leading zero.
Is it “10-year-old” or “10 year old”?
Use hyphens when it’s used as an adjective: 10-year-old boy.
What’s the rule for writing years?
Use numerals only: 2025, not two thousand twenty-five.
Conclusion
Mastering the art of writing numbers isn’t just about memorizing rules it’s about understanding what makes writing clear and polished. Whether you’re handling fractions in writing, formatting money amounts, or managing style guide differences, the goal is always the same: clarity and consistency.
Choose a style (like AP or Chicago), stick with it, and always consider your reader. Well-written numbers build trust, look professional, and make your message easier to absorb. And when in doubt keep it simple, clean, and readable.
