When to Write Numbers as Words: Rules for Legal & Formal Documents

Published March 9, 2026 · 9 min read

Should you write "7" or "seven"? "1,250" or "one thousand two hundred fifty"? The answer depends on context, and getting it wrong can range from a minor style violation to a legal vulnerability. This guide covers the major style rules for numbers in writing, with special attention to legal and financial documents where precision is not optional.

The Major Style Guides at a Glance

Different style guides have different thresholds for when to spell out numbers. Here are the most widely used:

AP Style (Associated Press)

Used by most newspapers, magazines, and online journalism:

• Spell out numbers one through nine
• Use digits for 10 and above
• Always spell out a number that begins a sentence: "Twelve people attended" not "12 people attended"
• Use digits for ages, dates, percentages, and measurements even if under 10

Chicago Manual of Style

The standard for book publishing, academic writing, and many organizations:

• Spell out numbers zero through one hundred
• Spell out round numbers: two hundred, three thousand, one million
• Use digits for numbers above one hundred that are not round: 103, 1,547
• Always spell out numbers at the start of a sentence

MLA Style (Modern Language Association)

Common in humanities and literature:

• Spell out numbers that can be written in one or two words: three, fifteen, one hundred, two thousand
• Use digits for numbers that would require three or more words: 101, 2,753

APA Style (American Psychological Association)

Standard in social sciences and scientific writing:

• Use digits for 10 and above
• Spell out numbers below 10
• Use digits for numbers in tables, statistics, mathematical contexts, and measurements regardless of size

Universal Rules (All Style Guides Agree)

Despite their differences, all major style guides share several rules:

Always Spell Out Numbers at the Start of a Sentence

"Four hundred fifty employees attended the meeting" — never "450 employees attended the meeting." If the number is unwieldy, restructure the sentence: "The meeting drew 450 employees."

Be Consistent Within a Sentence or Passage

If a sentence contains multiple numbers in the same category, treat them the same way: "The study included 8 men and 12 women" (not "eight men and 12 women"). When numbers from different categories appear together, each follows its own rule.

Use Digits for Dates, Addresses, and Page Numbers

These are always written as digits: "March 9, 2026," "42 Main Street," "page 7."

Spell Out Common Fractions

"Two-thirds of respondents agreed" is standard across all guides. Decimal fractions use digits: "0.75 inches."

Numbers in Legal Documents

Legal writing has its own conventions that override all style guides. The stakes are higher: ambiguity in a contract, deed, or court filing can lead to litigation.

The Belt-and-Suspenders Convention

The most distinctive legal convention is writing the number both in words and in digits. The written-out form comes first, followed by the numeric form in parentheses:

• "One Thousand Two Hundred Fifty Dollars ($1,250.00)"
• "Thirty (30) days after the effective date"
• "Seven Hundred Fifty Thousand Dollars ($750,000.00)"

This dual representation exists because of the legal principle that words control over figures. If someone alters the digit "750,000" to "7,500,000" by adding a digit, the written form "Seven Hundred Fifty Thousand" still governs. The same principle applies to checks, where the bank honors the written amount over the numeric amount.

Capitalization in Legal Amounts

In legal documents, dollar amounts written in words are often capitalized: "Three Hundred Thousand Dollars ($300,000.00)." This is a convention, not a legal requirement, but it increases clarity and makes the amount stand out in dense contract language.

Always Include Cents

Legal amounts always include cents, even for round numbers: "$5,000.00" not "$5,000." The ".00" eliminates any possibility of cents being added fraudulently. Similarly, the written form includes the cents: "Five Thousand and 00/100 Dollars" on checks, or "Five Thousand Dollars ($5,000.00)" in contracts.

Dates in Legal Documents

Legal documents typically spell out dates fully: "the ninth day of March, Two Thousand Twenty-Six" or at minimum include the full month name with no abbreviation: "March 9, 2026." Abbreviated dates like "3/9/26" are ambiguous (is that March 9 or September 3? Is the year 2026 or 1926?) and should never appear in legal documents.

Why Legal Documents Spell Out Numbers

The practice of writing numbers as words in legal documents is not mere tradition. There are concrete reasons:

Fraud Prevention

Digits are easier to alter than words. Changing "$1,000" to "$11,000" requires adding a single character. Changing "One Thousand" to "Eleven Thousand" requires rewriting an entire word — a much more detectable alteration. This is why the written amount on a check is the legally binding one.

Clarity and Disambiguation

Is "$1250" one thousand two hundred fifty, or twelve dollars and fifty cents with a missing decimal point? The written form eliminates any ambiguity. International readers may interpret digit grouping differently: "1.250" means one and a quarter in the US but one thousand two hundred fifty in Germany.

Historical Practice

Before typewriters and computers, legal documents were handwritten. In handwriting, digits like 1 and 7, or 3 and 8, can look similar. Spelling out numbers eliminated this source of error. The convention persisted because the underlying reason — preventing ambiguity — remains valid.

Numbers in Financial Documents

Beyond legal contracts, several financial contexts have their own conventions:

Checks

The written dollar amount line is legally controlling. Always fill the entire line and draw a line through remaining space. See our complete check-writing guide for step-by-step instructions and examples.

Invoices and Receipts

Invoices use digits for amounts, with two decimal places always shown. Words are not required but may appear on formal invoices for large amounts. Currency symbols or codes should be explicit: "$1,250.00 USD."

Tax Documents

Tax forms use digits exclusively. Do not spell out numbers on tax returns. Round to whole dollars when permitted, and follow the specific form's instructions for each field.

Real Estate Documents

Purchase agreements, deeds, and mortgage documents use the belt-and-suspenders approach for all monetary amounts and for key quantities like property dimensions and acreage.

International Conventions

Number formatting varies significantly around the world, which matters for international contracts and documents:

In international legal documents, always specify the number format or use the written form to eliminate any ambiguity.

Quick Reference: When to Spell Out Numbers

Here is a practical decision tree for everyday writing:

• Legal documents: Always spell out AND include digits in parentheses
• Checks: Always spell out the dollar amount (see how to write a check)
• Beginning of a sentence: Always spell out
• Journalism (AP Style): Spell out one through nine
• Books and formal writing (Chicago): Spell out zero through one hundred and round numbers
• Scientific writing (APA): Spell out below ten
• Casual writing: Be consistent; when in doubt, spell out small numbers

Need to convert a specific number to words? Use our number-to-words converter for instant, accurate results. For large numbers beyond everyday use, check out our guide to the names of large numbers.