Legal documents can range from bank checks to bills of sale to depositions and court-issued judgments. The risk of ambiguity makes it a good practice to include not just accurate and precise amounts and numerals, but to include the written number as well. Although bank checks may not be used as often nowadays, that's where most people have seen written-out numbers to ensure there is no mistaking the amount of the check.
Associated Press Style
The Associated Press (AP) Stylebook contains guidance on how to write out numerals, but the average person who writes a check probably isn't going to realize there is such a book, nor would she consult a book before writing a check. It's not necessarily because writing checks are such a common practice, or at least it once was, it's that writing out the numerals is common. As an example, if you're writing a check for $107.53, you would write on the line below the payee's name, One Hundred Seven and 53/100. You may use numerals for the cents portion of the amount, and draw a line from that to the preprinted word Dollars.
Legal documents such as settlement agreements may have five-to-seven-figure amounts that you will need to carefully write. The surrounding text for a settlement agreement differs from a bank check, and there may be more than one section of the agreement where you need to write out a dollar figure, so review the document to avoid leaving blank spaces where the written-out amount should be. For example, a settlement agreement for $1,250,001 million would typically be enclosed in parentheses and written out as: "One Million, Two Hundred Fifty Thousand and One Dollar and no/100." In its presentation about marital settlements, the American Bar Association suggests writing $36,000.00 as "thirty-six thousand dollars exactly," which is a very streamlined way to verify the dollar amount in writing.
Law Firm Policy
Your law firm might have a specific rule for writing out numerals, and in that case, you should follow the examples provided to you. However, in the event that you are crafting a legal document and don't have a model, use the standard rule for writing out numerals and hyphenating numerals that are part of a larger amount. For example, $50,323.75 should be written as "Fifty Thousand, Three Hundred Twenty-Three Dollars and 75/100 Cents." Capitalize the letters and hyphenate the words for 23. In this example, you include the word Cents and use numerals for the portion of the dollar.
No Absolute Rule
If you're creating documents within your business, understand that there's no absolute rule for writing out an amount in dollars and cents. All you're really trying to achieve is clarity, so there's no doubt about the amount you're writing and no scope for dispute. Best practice is to write the amount in words, then follow it up with the numerical amount: ABC shall pay XYZ Two Million Dollars ($2,000,000). The idea here is that numbers are easier to read, but they are also much easier to mistype, for example, by transposing a couple of digits – $50,967 instead of $50,697. If there's a discrepancy, the words will prevail. For very large sums, writing "$6.8 million" or "$10.2 million" should do the trick, but you don't want to go beyond one decimal place or it will get confusing.