Number to Words

Why the written amount wins

The convention that words override digits on a financial instrument is centuries old and rests on a simple asymmetry: digits are compact and therefore fragile, words are redundant and therefore robust. Altering the numeral 100 to 900 needs one confident stroke of a pen. Altering the phrase 'one hundred' to 'nine hundred' requires forging several letters in matching handwriting, in a space that was not left for them. The same logic explains why cheques ask you to draw a line through the remaining blank space after the written amount — you are closing off the room in which someone could append 'and fifty thousand'. Every one of these small rituals is an anti-tampering measure that predates cryptography and still works.

Where else it is required

The practice extends well beyond cheques. Contracts routinely state a value twice — 'the sum of fifty thousand dollars ($50,000)' — so that a typo or an alteration in one form is caught by the other. Legal deeds, promissory notes, court filings, invoices for large sums and many statutory forms carry the same belt-and-braces requirement. It is not bureaucratic decoration. A misplaced decimal point in a contract is one of the more expensive typographical errors it is possible to make, and forcing the number to be written twice, in two different notations, is a remarkably cheap way of catching it before anyone signs.